You can use more than one account on an iPad. It is important to keep track of what you bought in each account, because you'll need to sign on with that account to update the app.
As for iCloud, you do not have to use the same Apple ID for iCloud as you do iTunes. That way you can have different store accounts for each person (if needed) and still have the same iCloud syncing. Or vice-versa.
Apple IDs and iCloud
And I am almost certain the device limit is 10 for iCloud and iTunes syncing. 5 is the number computers you can authorize on a single iTunes account.