"how much do you usually get paid for a show?"
every show is different. sometimes you "should" get paid and sometimes you "shouldn't". if you're the local band with the biggest draw on a show with no touring bands, then you should get something. if you're a local band on a show with smaller touring bands that don't have very big draws, then you should NOT get paid anything and all the money should go to the touring band. if you're a local band on a show with a really big touring band that has a really big draw, then you should get something.
"Do you take shows for free just to get publicity?"
i don't really like terms like "publicity" but essentially, yeah. if no one's ever heard of you, then you shouldn't expect someone would want to pay you to play a show for them. but also, don't just take whatever show you can. show some discretion and just play the good shows, where the other bands are good and where there will be a good crowd. if you play awful shows, i think the people there will just associate the awful feelings with you. play shows with good bands and if you don't get asked to play shows with good bands, then it's really easy to just book your own shows. i was playing all sorts of awful shows until i decided to start setting up shows for myself. the last three shows i've played have been with anamanaguchi, starscream, george and jonathan, zen albatross, and j. arthur keenes. inifinitely more fun and relatively easy to set up!
"How long is an average set? Thanks."
a lot of the time, the venue will let you know how long they want you to play. but i'd say that if you're not the main attraction, 30-40 minutes is about right. even if you've got decent songs but you play too long, people will get tired of it. you have to really like something to be able to listen to an hour of it in one sitting. i think 35 minutes feels like a nice full set but also doesn't feel annoyingly long.