Yes, Angelfish will be fine with being just one. And my Angels never bothered my guppies. The only fish that were ever a problem with my Angels were my male Sailfin molly (he jumped out of the tank, RIP) and my betta. I have a tank of Angels and I put some zebra danios with them, but they were chasing my Angels all the time so I moved them to another tank.
But guppies should be fine.
Hmm. Depends on the angelfish, I guess. I know for a fact that at least two of my angels regard guppies as an attractive snack. I never put any fish smaller than my angels' mouths in their tank. They'd eat them... not if, but when.