Thank you so much! I'm so happy to hear you're enjoying the game.
As for NPCs, I'd recommend having them function as another player character that the group can collectively run. The characters are simple enough that it's easy enough to do so with the help of the GM. That's how I've handled it in the past. If that's too much to handle, it could just be handled as a narrative boon, having them tag along with another cadet and granting them some drive or skill boost for specific tests..