EF,

The smaller size model is a good idea to get the system setup and 'feel' of flying it. The biggest consideration is the weight and bulk of the electronics. From the world of RC today, we can find a lot of small, light gizmos to use. There are people here, in the USA, who have done great work in electronic auxiliary controls - Fred Cronenwett among them.

I feel it is still best to use mechanical control of the elevator - the loads may be considerably heavier than on throttle, or in driving a servo for other functions. I also prefer the physical feel of elevator response...

As to small size, your estimated span sounds about right for modern .20-.25 engines. The modern engines are quite powerful for their size, too, so that's some help with carrying installation weight.

As mentioned, the USA's National Model Aviation Club: AMA, has a website where you can read (our domestic) competition rules for line diameter and type (i.e., solid or braided cable.) The CLPA (Stunt) rules on lines and pull standards are used generally for non-competition models which don't have specifications, and for sport flying that may not be to any specific event performance standards. For CL Scale events, AMA has pull test standards related to weight of the model. I don't have a set of the FAI rules handy, but they may differ from the AMA specs.

I believe that the metal core in an insulated line is what is measured, not the outside of the insulation. That makes sense. Also, and I think the FAI applies this, too, the coder/decoder pulse train is what is conducted down the lines to the model. NO radio frequency transmission!