First off, welcome to FT...

Secondly, your best bet would be to post in either the DL or NW forums as the upgrade processes have been discussed ad nauseum.

Thirdly, there is no domestic C class.

Fourthly (Is that actually a word?), and lastly, unless you buy a Y-up or other eligible full fare ticket, your 5,000 miles will be worth squat, as you won't get the UG.