The big stick is an excellent 2nd airplane after your trainer.

A basic radio will fill all your needs now, but if you can swing it I would get a JR computer radio. The XF 662 would be great for you. The radio will be perfect for your trainer, then just get a "flight pack" for the stick. Then you control both planes with one radio. Computer radios are great. There's so many mixing options and things you can use. You can reset your trims and control throws with the computer rather than messing with all the linkages (of course they have to be close first). Go with JR if you can.