Moderator, Marriott Bonvoy & FlyerTalk Evangelist
Join Date: Oct 2002
Location: McKinney, TX, USA
Programs: United Silver; AA Plat/2MM; Marriott LT Titanium; Hilton Gold
Posts: 11,727
Unfortunately, the room upgrade certs are only usable on a points/awards reservation. So no paying cash for a room and using points for an upgrade.
It is possible to go the other way though. Say you have a points/award room, it is possible to use cash to upgrade that room (as well as possibly use the 5K room upgrade awards.)
As for your second question, a 5K room upgrade award is for the next room level up. So when you want to use them, it is very possible you might need more than 1 per night to get the upgrade you want. For example, a base award room at a beach resort might only get you an inland view room, but if you want an oceanfront room, you might need 3 or 4 upgrades (1 might get you mountain views, the second might get you Oceanview, and so on.)