If I paid for my room already, when I arrive am I still going to have to put down a deposit?
Yes, the policy is that upon check in, they require a $100 deposit either in cash or on a card. My advice would be to go elsewhere. This is an absurd policy, and once you see the actual hotel, you'll agree it's a rip off.
I think they will ask for a credit card number to be on file for any charges that may be incurred during your stay. I would advise that you look for a more reputable place to stay though. I believe if you cancel your reservation in advance of your stay they should refund your deposit.
Get an answer from Quality Inn Kent staff and past guests.