Overall, I would say this is a basically okay episode. Starlight's wanting to find someone to act as vice headmare and assist her with running the school seems like a reasonable thing to do, and I don't take any significant issue with how the plot of the episode unfolds. Trixie is generally obnoxious, but she's almost always been that way to me, so that's kind of expected for me at this point. I'm not necessarily specifically excited about Octavia, Dr. Whooves, or Spoiled Rich, but their appearances in this episode are fine enough (and I wonder why we don't see Octavia, Dr. Whooves, or even Big Mac being considered to be teachers). And the selection of Sunburst to help Starlight with running the school seems like a good decision, although I'm not so convinced about having Trixie be the new student counselor, as I'll elaborate below.
To start off, I'll just talk a bit about the qualifications and fitness for candidates to help run or teach at the School of Friendship. I've said before that I don't think any of the Mane Eight are particularly qualified to be running a school, and that's been shown in the haphazard, and sometimes downright dangerous, way that the School of Friendship has been run so far. So Equestria seems to have different standards for qualification and fitness for a job like that, as compared to what we would probably have. But, by show standards, Sunburst is probably a pretty good choice to be vice headstallion. I wouldn't say that his knowing a lot about magic or whatever in itself means that he's qualified, but he seems generally competent, and might be able to rein in or calm down Starlight when necessary. I'm also surprised that Octavia, Dr. Whooves, and/or Big Mac aren't considered as teachers for the school (at least not on-screen). My impression is that the Mane Seven will be co-ruling Equestria, or will be assisting Twilight in ruling Equestria, so I would think that the School of Friendship is going to need new teachers. From what we see, Octavia seems like a perfectly fine music teacher/band director; Dr. Whooves is a little eccentric and/or absentminded, but probably could be a good, or at least passable, science teacher; and if Big Mac were willing to talk more, he probably wouldn't be a bad teacher, either, if he wanted to be.
However, I'm a lot less convinced of Trixie's qualifications to be the new student counselor, and whether those overcome her personality issues, poor judgment, lack of experience, not taking the job seriously, etc. Starlight says that Trixie (supposedly) cares about the students, and that Trixie stands by the ponies she cares about. The primary demonstration of this in the episode is that Trixie stuck up for Gallus to Grampa Gruff. But, for one thing, as I mention below, did Trixie really teach Gallus and get to know enough about him to stick up for him as a student? And Trixie mostly was yelling at Grampa Gruff to care more and be more involved in Gallus's life. That could be seen as something good to do (and perhaps something that needed to be done), but how often are situations like that going to come up? How often do student counselors need to "stick up for" students, and to whom? Their parents? The teachers/staff? Other students? Even if that might happen occasionally, that doesn't seem like a major role for a student counselor.
Another thing Starlight says is that Trixie helped Starlight talk through her problem, and Trixie "really did give good advice". But Trixie had just gotten done saying that she gave good advice when she didn't mean to. Shouldn't we want a student counselor who gives good advice intentionally and on purpose, not just when she doesn't mean to? And Trixie's happening to help Starlight talk through one problem doesn't necessarily mean that Trixie will be able to talk students through their problems, day-in, day-out, as a full-time job. Trixie also didn't seem to care about the subject matter being taught at the school, which would be a problem when the student counselor probably needs to help many students figure out what courses to take, what their paths to graduation will be, etc. For one final point, in the episode "Marks for Effort", Starlight offers the CMCs new jobs as tutors for the school, which seemed to imply that Starlight as the school's counselor was making staffing/hiring decisions. So does that mean that Trixie would be making staffing/hiring decisions for the school under headmare Starlight?
I don't really have any other big-picture observations, so here are the rest of my miscellaneous observations:
Starlight says that if Twilight is going to talk to her about leaving early yesterday, she didn't have any students on her schedule. So I suppose this confirms that Starlight doesn't have open-door office hours anymore, or at least not at the end of the day.
When Twilight tells Starlight "I can't think of anypony who'd be better for the job" of taking over the school, what exactly that means is a function of Twilight's knowledge and how much she thought about it. If Twilight doesn't actually know very many people (particularly school administrator types), or didn't think very hard about who would be good for the job, then that statement wouldn't necessarily mean much.
So Celestia and Luna are actually teaching Twilight at least some things before handing off the rulership of Equestria. At least they apparently are no longer just saying that the friendship journal written by Twilight & friends "is a better guide than any we could provide", and leaving Twilight & friends to figure everything out, although we'll have to see if the lessons like these end up being helpful or have any significant impact.
And Twilight almost seems to be denigrating the royal etiquette lesson, but, for example, if Twilight will have to deal with other societies like the yaks, who might get offended at improper etiquette and retaliate (in whatever way) as a result, then knowing proper etiquette would be important.
Doesn't "hiring" a vice headmare imply, you know, getting paid? This just raises the never-answered question of where funds for the school come from, and how transparent these hiring and spending decisions are to whomever is providing these funds.
Also, Starlight tells Spoiled Rich that fundraising is "not the primary responsibility of the vice headmare". So is fundraising a responsibility, just not a "primary" one? Starlight doesn't outright say that the School of Friendship doesn't do fundraising.
Starlight's tacked-on "...but anypony is welcome to apply!" makes me think: Is Starlight required to follow non-discrimination laws or the like in deciding whom to hire for a position? If Starlight rejected Spoiled Rich as a candidate without "due consideration", could Spoiled file a discrimination lawsuit against Starlight and/or the school?
Is it really a good idea to have band practice in a room that doesn't even look to have doors? Is it possible that the band might disturb people in other parts of the school nearby?
Every other vice principal candidate was teaching a class under the watch of one of the Mane Six (Big Mac with Rarity, Spoiled with Rainbow, Octavia with Pinkie, and Dr. Whooves with Fluttershy), so who's watching Trixie? Whose class is Trixie supposed to be teaching, and why doesn't the original teacher seem to be there?
I thought the idea behind parent-teacher conferences is that the teacher has been teaching the students for weeks or months, and therefore, the teacher knows about, and can tell students' parents about, how well their kids have been performing, what and how they can improve, etc. We've only seen these vice principal candidates each teach one class, so how would they know and be able to tell parents (with any specificity) how well their kids are doing? Are we meant to assume that these candidates have been teaching classes off-screen for weeks or months? Or is all of this just an exercise in how well the candidates can flatter students' parents without actually knowing or saying anything substantive?
How much should we read into Trixie's suggestion that "maybe we should find a different representative from Griffonstone to be Gallus's guardian"? Does Trixie know that Gallus doesn't have a permanent guardian?
Seriously, Silverstream's father doesn't know what "exuberant" and "enthusiastic" mean? These aren't particularly exotic words, and they're in a library - just go get a dictionary.
Throughout this episode, the job that Starlight is looking to fill is always referred to as "vice headmare", even when speaking to male candidates. Even when Starlight is talking to Big Mac in her office, she tells him "And if you aren't comfortable with that, vice headmare probably isn't the job for you". Is "headmare" supposed to be a gender-neutral term? Is the word "headstallion" not used? Could they not just use the terms "principal" or "headmaster"?
Is Octavia's cello-playing at the concert being amplified at all? I don't see any microphones or anything around her, and I might think that her playing would be drowned out by whatever's playing through the mega-speakers.
I can at least kind of see how Octavia's and Dr. Whooves's field trips might be used as a learning experience for the subjects that they teach. But Trixie was supposed to teach history, and I'm not really seeing how teleporting a (seemingly random) chunk of Froggy Bottom Bog into the classroom would really be a learning experience for a history class.
Trixie's teleporting a big piece of the bog, and even casting a magic bubble around herself as she teleports it in, does seem like pretty impressive magic for Trixie to be doing, since she hasn't seemed to be a powerful unicorn in the past.
Finally, Twilight does say near the beginning of the episode that she'll be moving to Canterlot, and assuming Spike moves with her, then Starlight would presumably have the castle to herself. But then, if Sunburst moves to Ponyville, will he be moving into the castle with Starlight? That seems like more shipping fuel. Also, it's too bad that the Tree of Harmony didn't know that Twilight would be moving to Canterlot and taking over the ruling of Equestria just a couple of years or so after the events of "Twilight's Kingdom"; otherwise, the Tree could have saved the effort of creating this whole new crystal castle in Ponyville.