I put another coat of spackle on the screw holes and the seams. All is looking good! Tomorrow morning it will be dry and I'll sand it and then put a coat of primer on the board. That is provided I don't see too many problems with the finish.
I've been forgetting to put the Wizdom tips and learnings on the bottom, so I promise to start doing it again. Somebody called me on it!
1. Use the 3/16th's tempered hardboard (or thicker) instead of the 1/8th due to the fact that it is hard to countersink for the screws on the 1/8th board, and the screws go all the way through.
2. Use a VERY flexible putty knife when applying spackle in order to keep the coating thin, thus reducing sanding. (Thanks, George for the tip! My putty knives are too thick and inflexible.)
3. Putting up long sheets of tempered hardboard is at least a two man job, and really a three man job. Women can apply for the job as well! Don't be afraid to ask for help.