Aloe Vera can be used in dreads to condition them, but it will not help the dreading process because it will coat the hair causing the dreads to have a hard time locking up.

Probably two. You will probably use a jar when you first start your dreads, and then get another one after the third month, and that jar will probably last a year, if not more.

Backcombing
When the dreads are new you will wax them about twice in the first week and not wash the dreads. In the second week you will wash the dreads once and wax them twice. In the third week you should start to wash your dreads twice a week, you will still wax your dreads twice in this week. And you will do the same in the fourth week. Once the dreads are about a month old you will want to wax them after you have washed them, make sure your dreads are dry before you wax them, otherwise you might get a mildew smell. Once your dreads are about 3 months old you will only want to wax them about once every week or two, it is always best to wax your dreads when they are clean.

Well that depends on what wax you are using, if you are using a pomade wax (like Murray's beeswax, which I do not recommend, they are greasy and they will make your dreads fall apart) you will have to use a lot because it does not hold the dreads together.
If you use the Let's Dred Wax, Dread Head, or Knotty Boy you will be using a finger full of wax on each dred (depending on how thick the dreads are and how long they are).

I've had my dreadlocks for over 4 years now, and I still use wax for little loose hairs, frizzes, and to condition them so they don't get brittle. But you will not have to wax them all the time, once they are about a year old.