nereas:There is however no such thing as a modern "tech BCD."
So, I must have missed the part where a backplate and wing ceased to be a Buoyancy Compensation Device.

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nereas:There is however no such thing as a modern "tech BCD."
Yes, get a simple single tank setup to begin with, but make it a BP/W. You won't regret doing that, although you almost certainly will have to come up with a solution for pockets to keep various necessary items in. All you'll have to buy when you get to technical diving is a doubles wing. Much easier than having to buy the backplate and harness and wing and get used to it all with the additional change of double tanks.
My only remaining question is whether the BP/W will turn out to be manageable on my upcoming Caribbean dive trip; I'm thinking I'll be fine.
Henrik