You seem to have figured out the pros/cons very well already.

I'm going to be practical and suggest you take the job and save some money (assuming you don't have tons of it already). You will need to survive a few months without income if you're going to work on a startup.

PS: Make sure you don't get too comfortable with your new job! Try to keep an inexpensive lifestyle or otherwise, you might never again get the courage to jump in startup land.