How to decide what openings to stick with? I've come to the conclusion that I'm at the point where it would be better for me to stick with a handful of openings I can know well as oppose to how I would normally just play quite a large range of openings. My question is how I would find out what openings suit me since I plan to constantly play them because honestly with so many openings it feels difficult to choose. For instance I can't decide whether I prefer e4 or d4? Also I don't really have an "official" repertoire against openings that aren't d4 or e4 such as g3/g6 or b3/b6 openings, is this an issue? I normally just follow opening principles (control the center, develop etc.) to get by those openings.
Yes, it is better if you concentrate on just a couple of openings. Even though it feels difficult to choose, you should know if you like closed positions (then, generally speaking, play 1. d4 as White, and choose e.g. French and the King's Indian as Black) or open positions (when it makes more sense to play 1. e4, and e.g. Sicilian and the Grünfeld). If you have no preference, check your results - play the openings which you were successful with in the past.

Although, to become a better chess player, you need to practice all types of positions. (But not all openings.)

To answer your last question: if your opponent plays an 'odd' opening, you should indeed be fine if you develop along the general principles (but watch out for sudden tactics).