Yeah I understand, atleast you have some national players lol, it is kinda weird for me to have all different players from diff countries. I guess I should scout so I can get some National players.
If I were you, I'd sit tight for a while. By your own admission, you've made a ton of transfers recently, and unless you can make a major upgrade at any position, it's not worth the effort to simply change nationalities. Train away for a season, and wait for a chance to improve one of your non-training positions. If, when that time comes, there's a USA player who fits your requirements and is priced evenly with a foreign player, pick the USA guy. Otherwise, it's not that much of a difference.
As a young team, you should be more interested in improving your team and arena than hoarding local players. Once you get into the higher divisions and start to really feel the number crunch due to salaries, the merch bonuses for local guys helps quite a bit.