When I got my GWS Tiger Moth I did the other way round. I got the TM some time after my glow plane, so all I had to do was to get a flight pack and make sure it was JR compatible.

However, you are doing it the RIGHT way round and have the advantage that the GWS trannies are now available.

I know that the tx is available in both +ve & -ve shift, so here's what I would do:

Tentatively decided now what radio you might like for if/when you get around to the glow powered planes then get the appropriate GWS tx to match.

That way you'll be able to control the Slowstick with the new radio when you get it (assuming you get the same channel).