Hello!
Do not worry about having different control horn sizes...it doesn't really matter as long as you have the hinge line at 90 degrees to the attachment point of the wire.
I have used wires on many different airplanes from sailplanes and scale to F3D Pylonracers and do recommend them as they are lighter than any other system and doesn't transfer vibrations to the servo as carbon rods or balsa rods do.
Do not worry about having the wires parallel...it doesn't matter ....you can have them crossed if you like..and that makes the exit holes smaller.
I always try to mount my elevator horns inside the fuselage ...for looks only.
I often silver solder the elevator horn from soft 1,5mm thick iron and 3mm piano wire.
But now and then I use aluminum EATON arrows as elevator linkage to which I drill,CA glue and a solder 3mm piano wire (6cm-10cm long), to which I secure the control wire.
The wires i use are bought at a sport fishing store, thinnest possible fishing wire.
See pictures of my GP GEE BEE R-2

Regards!
Jan K
Sweden