I would not suggest creating a new apple id with the iCloud email address if you have already made purchases with your current apple id. The reason why is you can't merge Apple ID's so you will have to manage 2 apple id accounts with purchases on both accounts and in the end it gets very confusing and will eventually create a problem.
My suggestion is to just keep the current apple id account if you have already made purchases with it and convert that account into an iCloud account.
If you haven't made purchases with the current Apple id then don't worry about it. You should be able to use the iCloud email address as an apple id (it should be an apple id already) even if it is an alternative email address for another apple id.
Hope that helps.