Sounds like pretty close to a standard Ringmaster in size.  I am guessing 55' to 60' limes.  Any U-control ship in the 35 motor class should work on 60' lines.  .012 dia lines should work.  Smaller are hard to handle.  Larger have to much drag.  Beings you are going electric you may want to consider an RC throttle.  This would allow you to stop flying if things go wrong.  Sounds like you already have the RC radio and know how to hook it up. Hang the Tx on your belt and work the stick with your left hand.  Or you can have an assistant work the throttle.  Electric is quite so you can easily talk to a helper on the side line

Welcome back from the dark side of RC.  I too went RC for years and am now back.

 

There's two nice things about using an RC throttle: stopping when you get dizzy, and touch & go landings.  Neither of these are provided by a timer.  Neither are necessary (or allowed) in competition stunt, but for sport flying they're kinda fun.

Thanks for the info.
That is what I was going to do, have a small TX from a micro plane and micro rx, but am wondering if this might be a better idea:
 The KR Governor Timer Ver.2

I have one of the KR Governor Timers and I love it.  Coupled with a cheep speed controller it provides a bullet proof setup.  No burnouts if you hang the prop on take off.  However if you have the RC setup I would start with it.  It is an easy swap over when ready for a timer.  You will out grow the trainer in a hurry and be looking for an airplane that does the full stunt pattern.