I suppose that makes sense. Don't bother boosting RES, though. It's really, really unnecessary, especially since you'll almost always have new places that can be developed for 9~12 RES, maybe even less.

As for defense, that's different. When one of your territories gets attacked (or when enemies launch a counterattack, which reverses the progress you made on taking over that area - yes taking an area requires a few fights - if they win), you pick a team of characters to fight. Maximum of 5. Who you use for research (which, by the way, is exploration in the Japanese version) doesn't matter for defense more than anything else does. If you use anyone in a battle or for research, they can't get in another battle until the start of your next turn.

Yes this is precisely as problematic as it sounds.