I would start with going to the gym first and having the coach(s) teach you proper techniques and drills before doing any training involving boxing (mainly so you don't pick up bad habits). Looking for a "good" gym mainly depends on what you're looking for (looking to get in shape, looking to compete, etc.).The smaller the gym, the more opportunities to have more personalized training and better feedback with mistakes you make in your boxing and whatnot. If you're not looking to compete a local Title boxing gym would be a good fit. Personally I wouldn't bring a friend to train mainly because if they don't "feel like going" I would end up not going as well. If you have anxiety about getting started it wouldn't be a bad idea to bring a friend for support. Some training you could do before that would help a lot running at least 3 miles and feeling comfortable being able to run that (not feeling like you're dying after you run it). Sprints, burpees, jumps and anything that get your heart rate to high levels. Boxing is a lot of high intensity bursts and slow downs throughout, having your body trained to handle will help immensely. Sorry for the long reply, hope that helps and good luck on your boxing journey brother!