I would start in a 7mm wetsuit and work from there - it is a pretty good baseline from which to gauge how warm/cold you will be. You probably won't get incredibly hot or cold in it (to the point at which hypo or hyperthermia is an issue) but you will probably see which way your tendency is.Thanks so much for all this information! I still feel like I don't want to buy a wetsuit until I see how I handle water temperature out here. I've seen suggestions for 7mm or warmer for Catalina, while others are comfortable in much less. I'd like to get the thinnest suit I can get away with comfortable, and am fairly tolerant of 'cold'.
I found some threads about BP/W and read a lot about (and by) DSS. I'll probably go that route, and can always modify or get a more anatomical harness and pads if I think I'll need it (which I'm almost positive I will, based on backpack experience and all the damage I've done to my poor body over the years). I found this 'flex harness conversion kit' which looks interesting, albeit expensive for what it is? I don't know why I wouldn't be able to rig one up myself...
HOG Deluxe Flex Harness Conversion Kit - Accessories - Products
I'd say I'm over trying to own some inexpensive setup to get started with. I'll start looking for gear I think I'd actually like to own and can get some feedback on that
I do want to service my own regs at some point, but I think it's important to start out with something that works out of the box. I don't want to be preoccupied with thinking about how well or how much better my reg could be working while I'm learning to live underwater.
I would go for the BP&W without pads etc. Remember that you will only be using it for a very limited time above surface (shore entry or walking to the side of the boat) so the comfort of the harness on the surface is a (relatively) minor issue - the fit underwater is far more important. I bought mine 2 dives after my OW course (I wish I had had it during the course as it was so much more comfortable to dive in than the jacket).
Getting a cheapish set of new regs that you can service yourself in the future might be your best idea at the moment - you know they will work atm but you have the knowledge that, when it comes time to service them, that that is a possibility.