You may be confusing your 'devices' with 'Computer Authorisations'
You can have as many devices such as ipods, ipad, iphones without worrying.
Its the iTunes log in to buy music which is limited to only 5 at any one time.
It wouldnt harm in deactivating first, but if you didnt, it wouldnt be a problem, you have 5 to use and when you have used them all, lets say on different laptops or computers there is an option to cancel all and start over.