how many apple ids can I have on one icloud account

I have one apple ID. My iphone is linked to this apple ID and so is our Ipad. The ipad gets all of my mail, but also gets all of my text messages. This is not the greatest situation. When my husband got his work iphone, he was told to use my apple id so he would have access to all of my music and purchased items. That really messed things up because he was getting all of my mail and suddenly all of our contacts were shared. Not good!

We are now trying to set up a new ipod touch for one of the kids. Don't want the same situation as above. I want this to have a separate identity but still be on our account so it can share all of my apple purchases.

What is the best way to do this? I briefly talked to someone at the apple store a few months back and he said that you can have multiple apple ids on one account. Anyone have any tips on setting these up? Want to avoid any unnecessary newbie mistakes.