Two... to answer your question about Thrifty. Yes, Hertz owns them now, and supplies them with vehicles coming out of Hertz. So, they MAY have higher mileage or greater wear and tear.
Sign up for free as a "Blue Chip" member. Orlando is a "Choice Service" location.
"Save even more time by bypassing the counter. Well put your name and parking space number on our monitors. If you want a different vehicle, just take the hang tag from your rear view mirror and pick one from the same car class. The choice is yours." That way you can be sure YOUR vehicle has low mileage, is clean and the right color!
I would not be concerned about any hold unless you are bumping up against your credit limit.
Helpful hint regarding rentals, be sure your insurance covers rental cars - call your agent to confirm. Many credit cards also will cover your insurance deductibles, in case an accident occurs. Bring your insurance card too!