The SIG LT-25 is a tail dragger kit. It has a 63 inch wing span (about the same as most 40 size ARF trainers) and is a light, strong plane. One instructor I know recommends the LT-25 (because it is a tail dragger) with an OS 40 LA. This 40 is similar in size and weight to the 25 FX but costs $25 less.

OS 25 FX weighs 8.8 ounces without muffler. It costs about $85
75.6mm distance from the backplate to drive washer
30mm width of engine neglecting engine mounting flanges
38mm distance between centers of the mounting holes

OS 40 LA weighs 9.5 ounces without muffler. It costs about $60
70.0mm distance from backplate to front of drive washer
32mm width of engine neglecting engine mounting flanges.
40.5mm distance between the centers of mounting holes.

Pretty much all current radio equipment is excellent quality. If you have the money I think a 6 channel computer radio is a good choice. Right now I have 3 planes and all can be flown with a standard 4 channel radio. Since I do have a computer transmitter, all 3 are programmed in the one transmitter. There are lots of good 6 channel choices:
Airtronics RD6000 Super
Futaba 6EXAS
Hitec Optic 6
JR 6102 ,
Polk Tracker III