You really are a newbie!!"1. when showing at the provider's, do i need to bring my own towel and toiletries?"
Usually, those items are provided. Bring your own only if you have a preference or have some phobia about using a stranger's personal items. Some guys bring their own toiletries so their SO won't suspect something (Why do you smell like Irish Spring when you showered with Dove soap in the morning?).
"2. after showering, do i get fully dressed or do i go out wrapped in my towel?"
Usually, you undress before going to the bathroom to shower. If you insist on undressing IN the bathroom and getting dressed again after the shower, she will think you are really strange (weirdo, oddball, psycho, nutjob). After the shower and drying yourself (or by her), you usually walk (or run) to the bedroom in your birthday suit unless it is a "shared" bathroom and/or "other" people (the other monger) may accidently see you. If it is a "shared" bathroom or you have to walk through a hallway, you usually go back to the bathroom (as you went in) wrapped in a towel.
"3. do i bring my own condoms?"
Generally, theirs are better IMO. Let them pay for them. Theirs are infinitely better than Trojans. You could bring your own if you have a preference or are extra big.
"4. if i pop after 15 minutes (or five), what happens to the rest of the 1 hr session? must i leave immediately?"
The RA will usually pace the session to get the number of pops she usually allows. If she usually does MSOG, she will try to get the first pop done as quickly as possible. Many (most) RAs in SF Bay Area are one pop per session and the RA will pace the session accordingly. If you pop too soon, some RAs will feel sorry for you and allow a 2nd pop. Otherwise, the rest of the session will be filled out with talking, DFK/LK, cuddling, and/or massage (even a quick nap).
If this were a session with a SW, you leave as soon as you pop. Same with a AMP/TAMP/MP (at least, that's what you did the last time I was at a MP over 30 years ago).