Plan to stay at a Marriott property for two days already have a backup booking (flexible).

Checked the THC site, same hotel, same day, the prepaid rate is $4/night more, and the flexible rate is about 20/day more.

Two questions:
1. Is prepaid rate at THC counted as stay credit in Marriott?
2. What format of $100 credit would be issued? Would that reflect anywhere in writing? I'm counting that $100 otherwise the rebooking would not make any sense. It is a Four Point, so I'm not seeing anything fancy being provided as "experience".
3. The term said “Bookings must be made using an eligible Card and must be paid using that Card, or another American Express®Card, in the eligible Card Member's name”， Does it work if I book with the amex gold and pay with Marriot Brilliant? Or the charge needs to be on eligible card (Amex Gold)

Thanks a lot.