Can I sync my iTunes account with multiple devices?
Well yes you can. I find this method, and it has been talked about before, good for families.
What I have done is I have my main account, this is where I purchase movies and TV shows for the family to watch. This is the account that everyone logs into on their iPhones in the store for the stuff listed above along with games.
Next I have everyone create their own iTunes account for stuff like email and calendar events along with their separate contacts. This keeps everyones email, contacts and calendar separate while the main account allows everyone to share the movies, TV shows and games. Also everyone in my family uses iCloud so sharing calendars is a breeze.
This works out best if you do this from the beginning, instead of trying it with already established accounts. It can be done just a lot of work to get everything worked out.