Humping can express a lot of things. It can be a self-soothing mechanism, like scratching, or sniffing the ground. Here's a good article on dominance:
The Macho Myth | Dog Star Daily
However, most people don't enjoy being humped, so certainly, if she tries to hump you, tell her "no", and push her off.
The paw on top of the hand might be sass... on the other hand, my dog, who is quite submissive, does this when he wants to play. It is a "challenging" gesture, but it depends on the context.
With regard to stairs, it does take puppies a little while to understand height, just like babies... maybe shes nervous about going up them? If you pick her up, she'll probably learn to wait you out. Maybe try tossing a treat a few steps up - that should motivate her to move.
