Have you considered routing coolant from the heater core? This could eliminate the need for an additional thermostat, but would require you to open the valve manually (adjust the cabin vent temp. setting) once the engine warmed up.
I'll also recommend Evans coolant, especially if you plan on exposing your coolant to exhaust temperatures.
And if you want to get really experimental you could consider building a heat pipe
Your project looks fun and I'm looking forward to seeing what you do with it