1) Yes, I've heard of wing dowls failing in flight, but usually because it ripped through the top of the fuse that was built wrong. It's far more common for someone to not put enough rubber bands on there, and have the rubber bands fail, with obvious result. So, don't worry, those kit provided dowls will do the job. (what's the kit? If it's a even half-well designed kit, then you've nothing to worry about)

2) APC only makes nylon as far as I know. Don't worry about the instructions saying to use wood. APC props are actually fairly fragile, espeically near the tips, because they are so thin. And they are sharp, as you noticed. For learning, I usually recommend the black Master Airscrew props, you'll break less of them. Wood props probibly break easiest on things like nose-overs or rough landings, with APC in between wood and MAS

3) There are several differnet brands of weighed prop nuts. Some of them are used instead of a spinner, and work with the electric starter just as well.

They are NOT all the same size. Differenet engines in different sizes by different companies use different threads on the crankshaft. Some are english, some are metric, etc. So you have to make sure that whatever you buy will work with your engine. If the engine instructions don't say what the crankshaft threads are, post what your engine is, and someone here might know, or ask in the engines forum.