So, there's several issues I have with this character. I'll list them in no particular order.
First, considering the social circles he moves in, how on earth does he generate any attention if he's a quiet figure? What rumors or reputation does (or even, can) he have with such a wallflower personality? I'm from a well to do family, have attended large 100-200+ parties and no family scion is really rewarded for being so bland. It's a large disconnect, which I don't understand.
Considering his age and social status, I'm curious to know why he enlisted at age 25. Most enlisted Marines are late teens, early twenties, usually as an attempt to escape gang-warfare or send money home or just out of sheer, bloody patriotism. Any older usually means an extenuating circumstance. That was before independence so his original enlistment would be with the Star Army of Yamatai. And why he needs money if dad pays for his fancy tech.
Then enlisted at 25. Currently 32. What's he been doing for 7 years as a Santo-hei/P3C? Most characters get promoted by their second combat mission. It's very hard to remain as P3C for 7 years.
I don't allow starter characters to be a sniper. Without knowing their style, it could end very badly. Too much has been done that romanticizes sniping so its not a risk I'm willing to take. Also, most combat in 4th Fleet is CQB. If you're shooting at long-ranges (50m+), you're depending on the power armor's systems more than any real skill. Then there's also the fact that your average power armor weapon has the same (or greater) range as a modern anti-materiel rifle.
which he has grown used to exploiting. As such, John can manipulate non-hostiles if he has to by deliberately causing and exploiting awkward situations.
This makes him sound like a weasel. Which makes me think this may cause hostility towards the character as there are a lot of straight-shooting Marines in 4th Fleet.
Overall, I think this character is trying to be more than a starting character but missing all of the essential pieces to justify being more than a starting character. History doesn't add up. Personality and background are just odd. It's a good start but it doesn't sound Nepleslian to me.
Character mods, please feel free to chime in with your own suggestions.