sophistikate
One thing I would like to ask about:
I'm about to leave my job to go full-time for this start up but I'm not leaving my job on good terms. Will this be a big deal? I feel like by the time I apply in a few years, this job will be such a small part of my story that it won't even matter. Long story short, I felt really disrespected at this company and was treated poorly so I started performing poorly and basically am playing a waiting game (I have to stay 1 year or else I give back my signing bonus).
Hey dude,
So first of all, best of luck with your startup! You seem like a smart and very ambitious person, and it seems like you have your path set out for you.
The obvious thing, is to do as well as you can with your startup - find real partners, get angel investment, and succeed. But you don't need me to tell you that.

Other than that, make sure you keep up at least one activity and one volunteer work for the duration of the time. If you have time to run fundraisers or get involved in politics, then even better! Additionally, seek out any leadership opportunities you can get anywhere.
Those are the main overall things.
R.e. your job, do what you can there. And if you can try and preserve one manager who is your friend, at least personally, because they will come in useful when it comes time to getting your recommendation letters. And even if you aren't happy, don't burn your bridges! Bear out the year with a smile and leave with gratitude! In the long-term it will help greatly,
I hope these thoughts help, dude,
Best,
Jon