The fact that this isn't a fundamental requirement perplexes me. But I consider the generic silicon valley startup model a sickness. You sell your and the company's soul to VC's before you even make a dime at the expense of the people who sweat and bled for you and who you also promised stake, only to routinely get screwed by the VC's who get paid out first.
> * jump into bootstrapping full time while relying on personal savings
It can be done, but I don't recommend it.
> * bootstrap on the side while working a day job
This is what I did. About the time you're pulling your hair out because you don't have enough time in the day to follow through with taking people's money is a great time to finally quit that day job.