Alright, if you're going to be hunting zombies, I believe that you should put rate of fire as a higher priority than range. You probably won't want to have to reload your NF constantly as a hoard of zombies are closing in on you. Mavericks, longshots, and magstrikes would probably work best, as they are easy to find at your local Kmart, Wal-Mart, Target, or where ever you shop at.
I think your idea of a camo paint job would look cool especially if you did them in different schemes such as woods, desert, snow, urban, etc. It would add flair to the look of many guns. Good luck.
The use of an air compressor would ultimately defeat the purpose of taking off the original pump by sacrificing portability for a quicker reloading process. As Rover said, it would require you to plug the titan into the air compressor before each use. Providing that air compressors need to be plugged into a power source and they are quite cumbersome, using one during any sort of battle would be near impossible. I would honestly like to see you prove me wrong, although I highly doubt you will. Using bike pump is a good idea though.
Greetings my fellow Bay area nerfers! I am one of the two friends of Rover. This nerf war seems to be promising if it ever comes into fruition, and i absolutely look forward to it.