All your deductions are correct. The reason a methanol fuel runs cooler is because of its latent heat of evaporation and also the fact that an engine needs more methanol than it does gasoline. A richer engine of course runs cooler.

I would try using the original formula Gas/Glow fuel mix first, being sure of course, to use a good quality four stroke glow plug such as the OS "F" plug. For a custom "Four Stroke Gas/Glow Fuel Mix" you mention lowering the oil content in the glow fuel and raising the methanol content. The only way one could do this would be to buy the separate components of glow fuel, and custom mix them. Methanol, Nitro, oil, etc.

Sorry I just don't have time to experiment myself with all this, but will be very interested in hearing the results of your experimentation.

Good luck and have fun,
AV8TOR