I started with 4 accounts, then 5, and then 9, and when I realized that dps is lacking, I added last account last month.

To level up, I would suggest go with something that you enjoy, rather that rushing it. I am going to do the following to level up to 90.

- split my raid team into 2 x 5, doing quests at the same time, and alternate them between LFD.
- level up 8 x pandarian monks, with 2 boosters, using instances, quests and tagging. Play both teams at the same time also.

There are many threads here that talk about xp gained from instance and quests. Both are good. If you are using RAF, then perhaps someone else can advise you how to do it in the most efficient way for 10 toons.

Hope I answered your question, and have fun!