Stacking Existing N3048P Switches

Hello,

I have two N3048P switches which are already stacked together.  We have 3 other N3048P's installed in the same rack that for one reason or another are operating on their own and connected to the existing stack with SFP cables.  I'd like to add these three switches to the existing stack & have purchased the cables to do so.

Each switch has roughly the same config and carry the same vlans.  They're also all on the same firmware, boot and CPLD versions & I have backups for each switch already.

A couple of questions:

1. What happens to the port config of the 3 individual switches?  Will the ports just get renamed from Gi1/0/1 to Gi3/0/1, etc and retain their config?

2. Should I introduce one switch at a time to the stack or can I connect them all at once?

Any and all help appreciated!