I would recommend putting 100% on the startup for 3 months. I find that I can get a lot done if I put 100% of my time into anything for 3 months. You'll probably get enough done that people will be able to get an idea about what the product could become. By that time you'll either be able to find investors or realize that it's time to move on (or go back to full time consulting).

There is a reason the yc session is 3 months long. That's probably about all you'll need to prove your concept. Save up the bare minimum you need to survive and go. Good luck either way!