Welcome to the forums!
I'm right there with you on that awesome feeling of making something that flies.
I've done a couple conversions of kits for RC and think you're on the right track with that electronics set for the Lancer.
To create the control surfaces you'll need to add in an extra bit of framing where the hinge line will be. Doesn't need to be super heavy on a lightweight frame like this one. I'd say perhaps 3/16" wide on either side of the hinge - or just a stout 1/8" piece if you have a tougher stringer you can pull from.
In the case of the vertical, I'd say lay a straight edge about 1/4" behind where the current vertical spar is and make the cut there - then either glue in a new vertical piece on each part, or just glue it all together with one extra wide piece of balsa and cut it down the middle to separate the parts.
On the horizontal stab, dealing with cutting those ribs now that they are in place can be tricky - but it's certainly possible. You could also just add on a flat piece of balsa off the trailing edge for the elevator, maybe 5/8" or 3/4" wide. Sure it'll change the lines of the airplane, but that's half the fun of custom building
No matter how you get to separating the control surfaces, you'll want to use either tape or covering film for the hinges. These Guillow's kits and other UMX sized planes are so small that both the weight/cutting to install hinges, as well as the air flow that creeps around the gap, create more problems than they are worth. I've got many little planes flying great for many years on either 3M Blenderm hinge tape, or just an extra 1/2" wide piece of covering ironed on to form the hinge.
And make sure to post more pics as you're working through this project - always great to see more balsa in the air
