To get the $500 GC, you MUST purchase a 5 day base ticket, so you can't change it to a 1 day tic. You can however get the 5 day base, and upgrade it to more days & add the extra options upon arrival.
A good option for your dining is to put the GC on your room bill, like you would a ccard, and then just pay with your KTTW card. That way you are billing back to the room, and only having to keep track of your KTTW card (which you need to get into the parks, anyway).