If I have 10 potions of say 10 points of poison, can I apply all 10 to my bow for 100 points of poison damage?

Nope. It will say "This weapon is already poisoned" or some such after the first one.

Not on the same shot. I don't know if the same potion will stack if you hit with it multiple times, however.

Nope, since you can only have one poison on a weapon at a time. I think self buff potions don't stack either but I'm not 100% sure on that one, never really tried it.

sorry for necro, but i searched and couldn't find the answer, does anyone know whether multiple poisons stack when applied to the enemy?

Poisoned weapon -> a hit -> opponent feels the poison and it wears off from the weapon. Newly poisoned weapon -> a hit -> opponent again feels the poison and it wears off from the weapon. The two (or more) used bottles of poison still could stack as long as they work for a certain duration. Do they? I doubt it, but I don't know.