#1 You can divide after shooting is over, and just about anytime after since your climate is mild.

#2 Any all purpose fertilizer like 30-30-30 or organic fertilizer if you prefer. I like to use a slow release granular formula 1 or 2 times a month until fall. Stop fertilizing a month or so before your autumn begins. You can also use miracle grow just about whenever you water.

#3 I wouldn't divide it at all, because as I understand, root bound plants are less likely to survive dividing. If you plant it in the ground it'll generate more mass, faster. Then it can be divided once its no longer root bound. Or you could increase the size of pot and allow for some new growth. Dividing it then will be more sucessful.

#4 I have no experience with salt water spray, so I cant help you with that.

#5 Phyllostachys thrive in full sun, but will tolerate some shade.

These are just my opinions, so look for as many sources of information as possible. Good luck