When you create the site collection, you have two options either create via powershell or Central admin.
- for that you need a account which is part of farm admin group on the central admin, use that account login to the central admin and create a site collection(s)
- Now when you create a site collection during that process it will ask
you the Primary and Secondary Site collection admin. You can give any
- Once site collection created successfully, you login on that site with
the account you mentioned during its creation. Now you can create
lists and libraries under that site collection.
So this is the process, Now the question is, can i use farm admin as Site collection admin. Short Answer Yes. You can use any domain account for this.
But as a Best Practice, it is highly recommended dont use that account as it is running SharePoint critical process i.e Central admin, SharePoint timer service etc. if for some reason use lock the account, SharePoint will be go down.