Is there a way to "reset" a run for NG+ without having the beat the whole game again? I assume that hitting new game resets my save as a whole so i'm not sure what to do in that regard.

Yeah! All of the NG+ runners have an NG+ file saved on a USB drive that we use. Basically, complete the game with everything you want for your run, then before starting the new Challenge Mode run, copy the current file from the system to a USB drive. This will become your reset file.

Check the description of this video http://www.speedrun.com/rac_ps4/guide/nyau2 Has a step by step process

Thank you all so much!