I'll throw my hat into the ring here. I'm a very new diver as well, so just recently I went through the same issues as the OP.
IMO
Buy:
-Boots - you'll appreciate a pair that actually fits your feet. In my experience most rental shops use fins that don't require boots. You'll want boots in Bonaire (I did a discover SCUBA there, very rocky beaches, not sandy beaches)
-Wet suit - Not sure if you've been told yet... everyone pees in their suits. Get a suit that fits you and be happy and warm while you dive (in a suit that only you've peed in)
-Cheap Computer (I just got a Zoop for Christmas, is it the best computer on the market, NO. Not even close. It's a $200 computer, nitrox compatible, with a battery I can replace. If I sell my Zoop used I could probably get $100 for it in a year, or keep it as a back up. Like others have said, renting a computer for a week will cost about 1/2 the price of a Zoop or Leonardo.
-Mask/ fins - You've already got these. Make sure they fit, I don't remember what fins you said you got, but I hope they require boots...
Rent:
-BC - Try on different styles, and brands. Find one you like and ask the dive op if you can use the same one all week. You'll learn what features it has, and what features you wish it had. Then go home, research BC's and BP/W's and make up you mind.
-Regs - Just rent them for now and keep an eye out for good deals on a brand/ make you really want.