Since you mention your age, there is a good chance you are just having a quarter life crisis (becoming more cynical, great South Park episode about it!)
Agree with everything said about taking your break, but I think you also should set your expectations properly. 2 years without a vacation when starting a business is not so much, it's actually pretty standard I think. So are 80 hour weeks and everybody else in th company making money except for you. I don't know any successful entrepreneurs that are not complete workaholics.
I regularly have to tell vendors that the "we want to grow with you" pitch doesn't work with big enterprises. We want cost to be CAPPED. The right pricing model is a no brained entry price point that grows to a reasonable price for all you can eat.
If you get a full scholarship then probably, that's usually the case though. The PhD will give you prestige and credibility if you start your own business, and will open some doors when you are looking for a job (but also close others). It will also set you back a few years from your goals, and the amount of money you will get with a PhD won't be more than with a MS. Best perk of having a PhD is working in academia, which can be a great life style: much lower stress, decent compensation, lots of vacation time and recognition.
That's a function of your expectations. People get sad when they don't win the lotto but they don't celebrate every day they don't get hit by a car. It's not the odds, it's the expectations that are off.
So it's hard do charge anything or much for OS/Systems because there are so many free tools (it doesn't take long at all to deploy ELK + metricbeat for example). I would concentrate on applications, but then you are competing with DD and Librato anyways, unless you can cover applications that they don't monitor because they are too complex (I can't think of any though). I think the questions more than what niche to go after is what added value can you provide.
It's not insanity. Since time invariance is more of an abstract construct than a natural occurrence, I think you all but but guarantees that the same action will eventually yield a different result.