You sure you meant to post this here mate ? Or should it be in my post on the 2018/19 season proposals ? If so I'll move it for you.
Anyway to answer your questions.
One week GB will be either first or second weeks of June. Now given I'm up North for the Northern Show it will almost certainly be second week, therefore 11th to 17th June inclusive.
RAF -100 ? Haven't thought about it in that detail yet, but my first instincts would be to make it as open and inclusive as possible. I'll leave the exact scope up to the membership/moderators to decide during the usual pre G.B. discussion period which I'll set up a month or so before the start. If people wanted to enter builds based on the premise that the R.A.F. never happened ? (continuation of R.F.C./R.N.A.S. perhaps) then I'll leave that one up to the membership to decide.