Don't. If you're looking to work as a physicist at a biomed or similar startup, a PhD probably looks better than an MS, but at a regular tech startup, you'd be surprised to find out that beyond the core employees, most people have average or below average experience/education. On a team of a dozen software engineers that I'm a member of, one has an MS, and it isn't in CS. Either way, if anything, I'd try and combine work and school.
No. I've been working in and out of startups for over a dozen years and I've seen or shown my transcripts since graduation.
I once heard someone say that physicists make for good programmers (@daksis, maybe, but he's also a physicist I think). There are many disciplines within programming, along with multiple business verticals, horizontals and angles by which to sell information. Explore (meetups?) the ones you find a) hard and b) interesting and get a good picture of what you may want to do when you finish school. Now is not the time to pound the pavement without a degree or start-now skills. Much less embark on a startup adventure if you don't have the experience or commitment.