Some key things to consider:
* What comp are you giving up?
* Will your options be worth more than Facebook/Google/Amazon/Apple RSUs?
* Can you even afford your options?
* Will the options ever be liquid?
* Are you willing to earn-out after an acquisition?
* Will you have to do extra work? Are you compensated for it?
Starting a startup is great and you totally should. But working at one is (on average) setting yourself up to be worse off financially than working elsewhere. Make that decision deliberately and consciously only after really running the numbers and thinking critically about it.