Don't know about that, but you are right about big cables for 12v. The lightest grade welding cable is ideal for the drop down the tower as it is very flexible and tough.

Other less flexible cable is perfectly ok for the rest of the run. For very long runs 12v does present problems but if the machine is not too far away things may not be as bad as you think. These common machines are run in stall mode in high winds with the speed clamped by the constant battery volts and some measure of resistance is needed to get the prop somewhere up on its power curve. With 12v there is hardly ever a problem but at higher voltages keeping the line resistance as low as possible is detrimental to the output and the temptation to include the necessary resistance in the alternator results in lots of stator heat.

There are other limitations with 12v that for big systems are more of a problem that the one off high initial cable cost. Anything over 1kW in terms of input or inverter load is better run at higher voltage.

Yes you can wind your stator for dual voltage if you want. The commonly suggested method is to wind with two wires in hand so that you can connect them in series for 24v or parallel for 12. I wouldn't do this on a high voltage machine as it puts the full machine potential between strands but at low voltages the modern wire will cope adequately.

My preferred method is to wind the stator in 2 halves both star connected in series for 24v and with two half winding stars feeding in parallel through separate rectifiers for 12v. Sadly this requires an even number of coils and doesn't work with the common 12 pole 9 coil stator.

If you can tolerate lots of leads and rectifiers you can use star for 24v and Jerry connection for 12v although if you choose the cut in speed for 12v it may run a bit stalled at 24v.