Disregard everything else that is draining your energy. Mind you studies and start-up but keep away from all other college activities except couple of them that help you unwind or give you the support you need. After you do this, you should be just fine really!
You can do all these things without giving up half a dozen years of your life. In fact, in the years it takes one to complete a PHD, so much more could have been done in the outside world. This is a reality. But if YOU were to do PHD even then, its most likely because you just want to. Its not because its as valuable in any way you at look it as 5 to 6 years of equally sustained efforts in the industries one is doing PHD for. That is at least my experience.
Abshir