Well, as someone who has worked in startups for three years. I think you should at least take on an internship with a startup to see how much you like working in a startup. There is a pretty big financial cost with going to grad school especially if you do a masters. I know that payrates for a person fresh out of a masters program is comparable to the payrate of an undergrad who worked for 2 to 3 years. My opinion is that getting some real world experience is always good before you start your own company.