cannoning?

i am currently 78 strength 75 attack 70 defense 68 slayer 74 range 47 prayer and use chaelder as a slayer master. i am thinking about getting a cannon for slayer, however i have allot of questions about it before i buy it.

firstly i would like to know what the normal amount of cannon balls per hour i will be using.

second, witch tasks are best to cannon and (if there is more then one spot) where should i go to do so?

third what tasks are most likely to make me back the money i use on the cannon balls?

and last, how great will the xp gain on tasks i use a cannon on be?

thanks for any help!