I love the idea of an incremental approach, but sometimes that is easier said then done..Here is how my accumulation of gear went..
Mask - I believe this is one key piece of equipment that absolutely has to fit. My divebuddy on my last trip didn’t bring hers and paid for it dearly, made her trip completely miserable as she couldn’t get a good seal.
Fins - for me, getting full foot fins that are comfortable is really tough. And just about any rental gear I have seen have been full foot.
Regulator - the first and second stage are fine, but then you get into the gauges and octo. If you are using a computer, do you need a full set of gauges as well? What type of computer do you buy? Also carrying a computer is much easier, where carrying your reg is much more difficult. then you have to make the call of Octo vs Air 2 on your BC. If you learned on the latter and want to go with that, then the BC comes into play immediately. If using rental BCs you need the Octo too.
BCD - Some of this depends on your size. If you are average size, this may not be an issue. But if you are larger or smaller than average, finding a rental BCD that is comfortable can be a challenge. Plus if you have to make the call on integrated weights. I know I prefer my integrated weights to a weight belt. And very few rentals have integrated weights.
Suits - this is another thing about rental wetsuits. there is a common phrase I heard when I first started diving. There are those divers that pee in their wetsuits and those that lie about it. I am not sure how true that exactly is, but something to think about when renting suits, who has worn it previously. Plus you get back to the sizing issue. I was pretty much told by my OW instructor that I would need a custom suit to get a proper fit. While that wasn’t truly the case, the odds of me finding a rental suit that fits me properly is pretty slim. The next challenge is what thickness suits do you need? I started with a 3mm & a 7mm. I have accesorized with 2 sets of gloves, 3 sets of booties, a hooded vest and a plain hood for different conditions. I have also since then been renting a dry suit.
Computer - can be very temperamental. And need to decide do you prefer a hose mount or wrist mount? Air integration or not? I started with a hose mount and then got a deal later on an AI wrist mount.
All of this in the last 2 years. Next up is we are talking about going to Truck/Palau in 2010. Part of build up for this gets into tech as some of the deeper dives require TDIs extended range diver. This means getting into a BP/W, doubles, and anything else that will require. Could I have anticipated this 100 dives & 18 months ago when I started buying gear? I don’t think so. As my diving evolves, so does my gear.
The idea of planning ahead, renting and avoiding duplication would have been great, but I haven’t been able for forsee where my diving is going to take me. I think in some ways, its the nature of the beast if you are really becoming more than just a casual, vacation diver.