what's some nice engine one can use to make games that is small
something like this but with more editing tools http://tululoo.com/
also how to make rotating castle effect like castelian https://en.wikipedia.org/wiki/Nebulus_(video_game)
depends what you want i guess
rpg maker is well the obvious uboachan choice for stuff like rpgs and stuff that doesn't require super complicated battle systems. You'd be better off in the long run learning a harder engine like godot, unity, unreal, etc since they have more transferable skills but if you really just want to stay simple you could use something like pixel game maker i suppose.
Seconding this recommendation. It's cross-platform, free and there is enough documentation.