Squirrel 41
In answer to Q1 - I don't believe the final choice of Dave variant for UK has yet been made. It's all intimately tied in with the bring-back KPP, hence the ongoing effort to try and get STORVL to work.
As far as Q2 is concerned, the limiting factors are the long-lead times required for the cats and arresting engines, whether we buy US C13 & Mk 7, resurrect the BS6 and DA2 or bet the farm on EMALS/EARS. If its steam, then the delivery of a plant to go in the lower hull build modules would need to happen by mid-2010 at the latest. The upper deck bits are slightly less critical (though not by much) as those units will probably start construction early 2010.
Probably all too late for QE, but possible for PoW. As QE will be flying GR9 till 2018, one might suggest she completes with a ramp, and on service entry of QE goes for a first reserve/refit period to get her fitted out.
In any case, for Dave to hit the required IOC dates, they need to make the decision within about a year from now, no later.