The Shearwater Petrel is an excellent computer and probably the favorite computer of tech divers. I have a Liquidvision Xeo which I'm very,very happy with. I see nothing wrong with buying a good tech computer ( which I've found are much easier to use than cheap rec computers,btw) and having the computer that will work for any level of diving to come.
Why spend $350 on a rec computer that doesn't have what you will need to go on to tech, then purchase a new,tech computer in short while? The other nice thing about Shearwater and Liquidvision computers is that they are kept up to date with software updates. So, they really do have a longer possible life as a modern computer than a cheaper computer that can't be updated.
The only benefit I can see of purchasing a rec computer first is to save some upfront money. The disadvantage is that money will be wasted, as that computer can only be used as a bottom timer when going into tech training.
Depending on the agency that you do tech training with, you are likely to start out with tables and a bottom timer, but most tech divers ( except the few, dedicated to tables) move up to computers in short order, especially when doing multiple dives on charters/Livaboards.
As far as the DSS wing/BP, its an excellent system and not that much more than the cheaper brands when you buy the full package. I went with a DSS because it was one of few systems that offered a short backplate. ( I'm 5'1"). However, I did switch to Halcyon. My husband purchased a Halcyon kit and I really liked the quality of the details. I'll either be selling my nearly new DSS rig, or maybe keeping it as a tropical setup.
I think the OP has made some outstanding choices. A couple of DRIS backup lights (500-1,000 lumen), maybe the inexpensive can light mentioned by Chrpai and the only thing left to buy, for a nice, single tank, DIR set-up, would possibly be a drysuit. That will depend on where you're diving, but most divers do end up with a drysuit for tech classes, if for no other reason that it gives them redundant bouyancy. It's also nice to have for longer, deeper dives, where the wetsuit isn't all that great at keeping you warm, due to compression.
---------- Post added September 1st, 2013 at 09:54 AM ----------
Can you please toss me example of what kind of gear costs that much? A rebreather? Because beside rebreather it seems that there isn't much extra gear besides maybe doubling/sidemounting tanks and stuff.
You will get a lot of different estimates but looks to me like you would be well on your way to being rigged up for your Intro-Tech and Advanced Nitrox/deco classes, other than a doubles wing. The biggest expense after that will be doubles tanks/manifolds and extra regulators. Still far less than $15,000.
I went through this recently as I decided I want to start doing tech classes. I've not even spent anywhere close to $5,000. I have a few things left to purchase ( doubles wing or sidemount, I'll probably switch to SM due to physical limitations, extra regulators). I already have a bunch of tanks so I'm good there and tanks can be purchased very easily on Craigslist, although you do need to pay for the VIP and probably hydro. Oh, I guess the valves need to be changed at some point, when I decide which tanks I'll use. Still, way under $5,000. I guess a $3,500 custom made drysuit would get you up there pretty quick, although I don't count mine, since I already had it for recreational diving. No, not sure how you could spend $15,000. $5,000 is generous.
Training,travel and gases could add up pretty quick,though.
