Garden Hose, your own or neighbors?
No, the chlorine will kill your plants.
algae will make water in a saltwater pool green If boosting the chlorine doesn't clear it up pool shops will have algaesides and floculants to the water clear again.
It is not likely, but it depends on what material the walls are made out of. Mud, probably not, but tile yes.
No ... the suns rays equally heat pool water regardless of what chemicals are used for keeping the water clean.