I think it is a great idea to buy a used board but then I'm an idiot because I bought a new waveski having never surfed one. I took me awhile to get the hang of it but I'm having a blast now. When I was learning to whitewater kayak I wasted a lot of time and money trying to learn on other boats. I couldn't consistently roll until I got my own kayak.
I was warned that many surfers hate kayakers but almost all the surfers I have met have been mellow and friendly folk. There are some rules that I follow.
1. Stay away from crowds you won't have the control that the experienced surfers have. As a beginner you will be perfectly happy with the less crowded smaller breaks.
2. Always check for guys paddling in before you launch and pass up on a wave if you fear a collision.
3. Look both ways before you launch so you won't drop in on someone. I had a guy drop in right in front of me once when I was kayaking. I put on the breaks and let the wave pass but he would have been the one hurt not me.
Surfline gives a nice travel report on breaks around the world. You can read up and get an idea of "the vibe" and crowd factor.
I recently paid a visit to the famous break on Sab. Inlet. You will understand why the vibe can be tense there when you see how aggressively the guys are surfing. They break all the rules I just mentioned and you will see many close calls. Anyone surfing there has to have board control or someone will get hurt.