I am thinking of joining USCF to get a FIDE rating. Is my chess.com rating a good starting point in USCF or are the ratings systems completely different?
Playing in USCF rated events will get you a USCF rating. The ONLY way to get a FIDE rating is by playing FIDE-rated players in a tournament big enough to be "dual-rated," such as major opens.
You have to play a minimal number of games against players with established FIDE ratings, I believe it is 9, within a certain period of time (so it can be over several tournaments, most opponents won't be FIDE-rated), at one time it was two years, and you must score at least one win among those games in order to get a FIDE rating.
And NO, Chess.com or any other online rating isn't comparable in any way. It is certainly fair to say Chess.com ratings seem higher on average based on skill level than USCF or FIDE ratings, but there is no way to accurately relate them. Different systems, different pools of participants, different rules (USCF/FIDE only rate games under official conditions, classical time controls, and with certified arbiters on site). Apples and oranges.
There are beginners and strong players in OTB tournaments. Your rating is fine to begin. Not so long ago there was no online chess and you could only play in tournaments or in clubs... so there's certainly no prerequisite of strength to enter a tournament. Large tournaments have class sections so you're able to play many players closer to your skills level (although you'd start by entering in the section for unrated players). It's the open section that has all the heavy hitters, so it's not like you'll be facing masters, grandmasteres, and people like this.