Hi!
Yes skip the temperature readings! Being a racer (Pylonracing ) I can assure you that no racer meassure the head temperature ...we set our engines by ear!
And that's the way all sport fliers should do too!

You must understand that most engines like some nitro. 5-10% nitro is all it takes to a have a all engines run just fine.
Running your engine on 0% nitro is no good. That makes it run hotter due to a much peakier high speed setting (Means it is more likely that the engine goes lean due to problems setting it right).

Ofcoarse you can use 14x8 prop on your engine! But remember doing so means you have to set the engine right (means setting it ritch so it will not overheat). But why use a 14x8 prop on a .75 engine??? A more suitable prop for sport flying is a 13x6,14x4 or 14x5N APC.
You have to choose the right prop for each airplane! That's very important!
Best props today are APC, Graupner Cam-prop or RAM. Avoid MA white tips props!!!

And do fix that carb! Silicon isn't the right way to solve the leaking carb problem!
Put in a larger screw in that hole securing the carb! I suspect it's a 3,5mm screw now. Use a 4mm screw instead!