iCloud and setting up as new

Hi - I plan to set up as new tomorrow on my new iphone. Upgrading from a 5S. I've been plagued with some software issues so seems to be the best way.

How here's my question...

If I set up as new, (and skip restore from itunes or icloud) can I later put in my icloud username and passwords to sync things like notes and contacts (possibly whatsapp,) or will I lose all of that?

I have a mac which has that stuff on it so I don't see all of it going right? Possibly whatsapp....

 

Any takers?

Would be greatly appreciated...