Welcome to the boards! I just bought my kit last year, and have a few ideas. Don't know how valid the are. I know lots of folks who dive a couple times a year, and rent their gear, but buy their regulators and gauges, because you want to know that the regs are right before you dive. Seems to me, I bought my mask (perscription lenses) snorkle and fins first, had some booties. Then a BC via the internet (Sea Dog Sports) and a tank (used from the Local Dive shop) and then plunged in and bought my regulators, computer and gauges, and such. After that, a drysuit and undies (early this year) and then sold the BC and bought a backplate system on eBay. Then a weight belt (had the weights) and then a different pair of fins (turtle fins for the drysuit). Then I bought a second tank, and am considering a third one. Since then, I have taken my console apart, put my computer on one wrist an my compass on the other and let the SPG hang on the end of the hose, re-rigged my backplate with new webbing and a release buckle on one shoulder strap, built suspenders for my weight belt and several other small things.
Don't think this is the 'proper' order, but it was the order things happened as the money became available and the equipment was found.
Good luck!