You said your GF is in school right now. If that's so, how will she move with you to SF? She won't be able to go to school (unless the school allows 100% telecommuting or she decides to take a semester off).
Remember that the $5,000 +$5,000n is an investment in YOUR COMPANY, not a paycheck. That money is meant to cover the founder's living expenses during the YC round. I think you will have a hard time using that money to live off of and support your GF.
If your GF can get a job and support herself (either while still going to school or by taking a semester off) I would say go for it. But if the only way is to send money back to FL then you are hurting your chances of succeeding, and I would find another way.
It's one thing to be fresh out of college with no debt and no responsibilities. I could imagine finding a roommate, eating ramen and stretching $5000 for 6 months or more.
However you sound a bit more like me. I'm 30, married, with $60,000 of student loans and a car payment living in Mountain View. In case you don't know what expenses are like out here, let's just say $5000 wouldn't even cover my loan payments + rent for 2 months. You will not find a decent one-bedroom under $1500. You can do better if you cram yourselves into an efficiency or get roommates, but just FYI, I got a 30% raise to move out here and I've never felt poorer. Given your situation, your runway will be shorter than most, but if you are good, that may be the extra drive you need to get something up and fundable in under 3 months. Me? I'm bootstrapping from someplace cheaper when I leave my current startup. I see the YC model as more appropriate for those with no experience, no connections and no responsibilities.
Remember that the $5,000 +$5,000n is an investment in YOUR COMPANY, not a paycheck. That money is meant to cover the founder's living expenses during the YC round. I think you will have a hard time using that money to live off of and support your GF.
If your GF can get a job and support herself (either while still going to school or by taking a semester off) I would say go for it. But if the only way is to send money back to FL then you are hurting your chances of succeeding, and I would find another way.