Let's see.... look at my sig, I have a fully fleshed out crew. I also now have a photonic bridge officer that I can't use unless I buy a slot.
Let's see... I role play. I have a Mirror Universe "alt" that runs around in the Mirror Universe outfit, leaving me with 2 slots, 1 with my Fleet Uniform and 1 with my off-duty outfit. So make up your own mind why I would need more outfit slots.
The only thing I don't really need right now is the ships.
You can delete on of you crew and save money.
You can only wear one uniform at a time and I don't know how you only have three uniform slots I have five.