I've always wanted to advance my RC building/flying skills enough to get into jet models, but I don't think I'd have the patience to go beyond "fun scale" standards.
My "upgrade" plan, when I stop moving around and have the time, will follow something like this:
Fly my great planes P-51 a while, build up some skill and experience with the retracts, etc. Possibly mod the model to have flaps, but I may save that for the next model.
Get a pattern-style plane to get used to flying fast. It must have retracts and flaps.
Get a hot sport plane to get used to fast/twitchy (optional step)
Build a generic semi-fast ducted fan, maybe one of those F-5 lookalike models. Some have 2 wing options for training and high speed. A used model would be fine here but I want some experience with intake and exhaust ducting before diving into a turbine build.
Build a generic turbine, no particular speed range required, just to get used to turbine ops. If it has enough wing to survive an engine failure, that would be best

Build a semi-scale F-15 turbine powered model, either 2 engine or one engine with split intake/exhaust ducting.
An F-18 would also be great but the moveable leading edge would be very difficult, the intake size is a little small, and I hate cheater holes. The moveable intakes of the F-15 would be almost impossible to duplicate so one of the non-scale portions would be having the intake ramps permanently drooped to an angle that matches the usual inflight position.