If you like the A4 then the Tamjets ARF version is also an option.

You will probably get mixed advice. There is no doubt that a trainer jet such as the Boomerang is a great first jet, however if approached correctly there is no reason that you can't have success with something a bit more scale.

That said, I believe the A4 has some 'interesting' characteristics which, although not insurmountable, might make your journey into turbines a little harder than it needs to be. I'm sure there will be some info on this if you search the forums. I seem to remember an YA A4 build thread somewhere that was powered by a Wren 44 Gold.