don't overthink, just grab a bar and start lifting
There probably are mean people at the gym, but generally, I feel like outside the gym people are generally meaner. Everyone's there to try and grow and work on themselves, most don't care for you at all. Don't sweat how you're gonna be perceived, just go there and work and sweat
keep it very simple until you're in the groove (meaning you go regularly), then slowly start adjusting and/or optimizing for whatever you're trying to accomplish exactly
listen to your body. When something hurts, try to really feel what exactly hurts and how. If anything but your muscles themselves hurt (joints especially), stop for now, you need either more time to adjust or you're doing something wrong. Try to figure out which one it is, by taking it easy and giving yourself some time anyway

there's a bunch of good resources linked in the c/fitness sidebar, you could take a look there for some of your questions - but I can't stress enough, how the most important thing is to just get into the habit of actually going there, anything else comes second. If obsessing about your split/workout will get you to go, have at it. If you just want to go and not care much for what exact plan your following, that's fine too, as long as you keep going. First few weeks/months is much more about building a habit and building the neurological capacity for certain exercises than anything else, really. Take it easy, keep going, listen to the signals your body sends you, keep refining and you'll be golden. It takes time, be patient

bit in a rush, sorry if this is a bit disjointed