can I have more than one apple id?

Yes, you can have as many as you would like. Each must have its own unique email address as primary of course. And purchases made on one are not transferrable to another, nor can any two be merged later on. You also cannot transfer or merge content between iCloud accounts created with separate AppleIDs.

You can have more than one iTunes account, but only one account can be logged in at any one time - it's generally best to have just the one account, all content that you download is permanently tied to that account (so only that account can do in-app purchases in an app, download updates to them, potentially redownload them, and authorise them on a new computer's iTunes)

Officially no. But some people with multiple computers have been known to create new IDs with each. It is frowned upon, particularly if it is used in the forums. Remember, although you may have a different ID, your style of writing can be seen for miles.