The only question I have is how heavy ga. wire to go from STC to power supply, and heat source. I'm using triple tap, b/c that's what's handy. That way, if I need to install an other fan, I'll have a ready outlet. My first build was similar, but used a bimetal thermostat. Hoping the STC will be more reliable, and the overall design will provide more consistent heat levels throughout the box.
I would say the wires on the extra triple taps you have would be plenty sufficient, but if you want a number, I would use stranded copper 16 ga. all the way.