There are a couple of ways to free the sticky throttle barrel. WD40 or a light penetrating oil would be first. Let it sit for about 30 mins and see if you can work it loose. Alcohol works better, but I would take the carb off first. You don't want to get alcohol inside the engine for very long as it can rust within hours. If those fail, pull the carb and put it into the oven at the lowest setting, and check every 5 mins. The heat will loosen the dried varnish.

If you have a hobby shop nearby, I would pick up some spare propellers. For the OS 40FP on a trainer, see if they have some 11-4 props. I bet it has a 10-6 on it. An 11-4 (11" by 4" pitch) or an 11-5 will keep the speed down for landing and maximize the thrust of the rather anemic 40FP. These are about $5 ea.

You also did not mention if the plane came with a charger for the Tx/Rx. If not, a new radio is looking better for you.

Did you get a glow-plug igniter? You can get a glow plug igniter at your local hobby store or online. I like the ones that take a dry cell battery. Speaking of glow plug, yes, they are black inside. The coil inside the glow plug will glow with the application of 1.2 to 1.5 volts