Mellisa, have the 7 pin installed, you can always buy a 7 to 4 adapter that plugs into your receptical if you end up with a trailer that has a flat 4 connector.
You are limited with the flat 4 as you will only have a ground wire, left and right turn and
tail lights.
You will not be able to run a brake line, charge line or backup
lights if you want to in the future.