Brazilian (everything off) hurts like a bitch. Bikini (only what's outside panty/bikini lines) barely hurts in comparison and is over in 2 seconds. The backside also hurts a lot less.
So If I were you I would just get those two things done, or just bikini for the first appointment if you're anxious.
If you have any sort of trimmer in the house (I use a beard trimmer) I would trim everything down before I go because it hurts more if the hairs are too long. Just be careful not to trim too short, I do about 7-8mm and never had a problem. Also helps with feeling a bit more comfortable. (Though trust me they've seen it all, they're not going to be shocked by longer hairs!)
Depends on personal preference but I feel a lot comfortable in a big impersonal chain than a small salon. The more clinical surroundings and the fact that they do it hundreds of times a week makes it feel like it's no big deal. Ofc the opposite might be true for you so think about what you want.
If you do go for Brazilian/more hair off, your skin might be surprisingly sore for a few days. For me it hurts even to use toilet paper. So you can get some things that help with that, moist toilet paper/wipes, a soothing/cooling cream, with hazel spray etc. Also jeans might hurt afterwards so wear a skirt and soft undies if you can.
The ibuprofen before does help but the most important thing is to stay distracted and not tense up. If you're not a chatty person, you could consider taking earbuds for music/podcast or can even watch something on your phone.
Most salons give you wipes to "freshen up" but you can also buy your own to use right before if you're worried.
One last tip, treat yourself to a nice lunch or drink afterwards! Really helps the pain 