I'd definitely start with the wetsuit. It's the most "personal" of all the items.. I don't really want to dive in something someone else peed in.
After that, I'd go with a BC. The BC you dive has the largest impact on how your gear is configured, how you're weighted, where you keep things, your trim, etc. Regulators are nice (and people will mention how they're life support equipment), but for the most part a reg is a reg. You screw one end on and breathe off the other end.
However, I'd encourage you to rent and dive as much as you can before buying a BC or a reg, so that you can decide what you want, what you like, don't like, etc.