He's a prince, yes. however, he comes from a military kingdom, meaning that everyone in the kingdom, even royalty, is expected to either be in the military or work in the factories building weapons. Prince Kronos was raised by the king and thus joined the royal military. Plus, Kronos insisted on starting at the FNG rank in the military. He wanted to prove to his "father" that he is strong enough to retain his status as a prince and as a legitimate kingdom soldier. Also, yes, he's half changeling, which he will learn about when he begins asking his "father" about who he really is when he starts tinkering with genetic codices. Also, Chrysalis abandoned him becase she had no preparation to deal with raising a foal, let alone have enough resources herself to nurture him. However, being the king's most trusted general, she discusses the arrangement and they both agreed to never tell Kronos about his parents until they felt that the time is right, and thus left him at the front door of the king's castle. His father was on what was supposed to be a routine sabotage mission. However, the remote detonator stopped working and he, along with a group of additional troops, volunteered to manually set off the bomb. On top of that, Kronos wasn't raised in the Crystal Empire, but rather a different kingdom altogether. Innovation and the drive to make himself and his father's kingdom stronger and more technologically superior are what drives him to sacrifice his body for these innovations. He also taught himself how to walk on his hind legs via physical therapy exercises and his first invention he implemented onto himself was the telepathy device, allowing him to work without the use of his limbs. He did eventually turn himself into the cyborg I made him into today. However, he's in constant physical, emotional and psychological pain all day and night. In fact, he's even afraid of his own mortality, so he refuses to sleep. Because of this, he compensates by putting his brain into "sleep mode" and has a backup power system in his mechanical body allowing him to perform his tasks unconsciously but accurately. This allows him to work and rest his brain at the same time. When he "wakes up", he tells the computer part of his brain to give a summary of the activities of his "night watch". Also, I guess you're right about the whole "terrifyingly heroic" name thing, but I guess the king just gave him a name that can invoke different emotions to other ponies depending on how you say his name and the context of which his name is mentioned. For example, depending on the context of any given conversation, anypony could portray him as a paladin or a harbinger.
Note: Sorry it took a week to reply to this. I'm in college right now and Friday is like the only day that I have no classes in. Also I've been getting nagged at by my family.