i don’t post art online very often but i have friends who would + do commissions so ik a bit
most artists would use paypal or ko-fi but cashapp and venmo are options for people living in the states i believe. if you’re not comfortable using your real name online i believe you can set up a ‘paypal for business’ account but i’m not sure about the terms and conditions of that
for your commissions you can base them on whatever feels right but imo you should at least be charging minimum wage. if a piece is gonna take you several hours you should make several hours worth of money at least imho! it’s a good idea to set prices and adjust accordingly over time with things like demand and such (i.e consider raising if too much demand, having deals or such if demand is lower etc)
the website you use is very much ymmv. if you draw anthro stuff furaffnity and reddit are probably best? for fandom stuff twitter and maybe tumblr. tbh every online platform has pros and cons, i’d say just cross post on as many platforms as you’d like
i haven’t got much other advice other than watch out for scammers (i think most people recommend half now half after the piece is done kind of things for this reason) and try not to take on too much at once so you don’t get burnt out on it