Now I'm not being rude here, and I'm certainly not asking you to heed my words if it's your dream to do such a thing. But commentaries are typically more enjoyable from someone with a lower-pitched voice, I'd wait a few more years if I were you.
And accents from all over the states are common in the media worldwide, so as for having a nice accent, I'd say it's a fairly common accent.
To reiterate, I'm not trying to dismiss your dreams if it's something that you yearn to do. But I'd advise waiting a bit longer.
Also, MLP is a very niche audience, are you sure you only want to commentate on that?
Now that's out of the way, I recommend getting yourself some video editing software if you fully intend to go through with it. You can line the audio up with the video very easy in most editing software. Sony Vegas is great if you can afford it.