I do a few dep gigs - 4 gigs with 3 bands this month. What they provide and expect can vary - usually a set list before the gig, sometimes with notes about keys and changes from the record. Sometimes I'll get a rehearsal but increasingly I'm less fussed about that. I try to make up a cheat sheet with minimal notes e.g. 2 sides of A4 per set, so I can have it on the floor like a set list.
I make a point of getting there before the band, helping with carrying and setting up PA and lights but holding back from interfering with how things are done. Use a very simple rig that I can set up fast, won't fail and then don't twiddle. I'm sure I get offered gigs because I'll be on time and act professionally rather than because of my playing.
Getting gigs is about networking and when bands on the local circuit know you do deps, you get offered more. I'd agree it might be easier to find a stand in guitarist for your band but it can be a lot of fun diving in at the deep end.