It is nice to think of the what ifs but in life you must take risks along with taking into consideration your short and long terms goals and seeing how they fit with your current and future financial situation.
1. Sounds nice in the short term, but in the long term you will no longer have income to pay your required bills, nothing for saving or investing with no guarantee that your degree will yield you the job you want in the end or that it will even be useful to you when you graduate as you may want to do something else a year from now.
Normally, people that have been their own boss don't do so well going backwards and working for someone else, especially if they were very successful at it. Yes, you might do OK for a little bit but eventually things will change as the working for others mentality is no longer a part of the type of person you are anymore. Normally this starts out with you thinking of little ideas or new products you could be working on, you start to see the big picture of what your current company is doing and how you could solve the problem better if you could do it yourself or build your own company and team to accomplish it. It starts small and that fire grows within you again. You normally don't see CEOs or other executives revert back to the regular employee roles because it is almost impossible for it to happen and if it does your normally miserable until your back in a role of leadership, innovation and risk taking.
Eventually the primal entrepreneurship spirit kicks in, and eventually you will git bored of the regular day job as you will want to lead things your way or with partners that have the same vision and are on the same path as you for the short and long term.
2. Long term it is always best to keep money coming in so you can invest it now so it will give you a nice return down the road. Depending on how much you invest and your employer contributes you could have an extra $30,000 or more for money down the road along with decreasing the total amount you are taxed for the year. Over time this adds up ($30,000+/year for 10 years = $300,000+) as soon as you stop contributing to your future investments, the growth of that number slows down. Sometimes you have do some of what you don't want to do for a little while so you can do what you want to do.
3. I would recommend going part time to school, working with your employer to see if they can possibly do tuition reimbursement, along with continuing to work on your side projects to help you find out what you have a higher interest in (or find another employer that offers what you want). Once you find something that interests you heavily and that you have experience in (your side projects count as experience) then apply for a job more in line with what you really want to do or start a company doing what you really want to do.
4. Since you have already owned and operated a business you know that starting another business will give you more freedom than you will ever have working for someone else. If you really want to have options you know you will need to start a business again and make it successful like your previous business. Though this time I would recommend making it more long term so it can feed you and fuel your projects, allow you to shape the full direction of the company, increase the income you receive the way you want, and allow you to be in control of your free time.
Yes, starting your company is normally the harder route but you have done it before and can do it again because you have experience doing it. In doing so you will have more time for your projects and can even use that time to insure they are bringing you money and growing your ideas. In the long term this is normally always better for you instead of working on on your employer's projects the bulk of your time while seeing very little financial profit from the large amount of time you put in vs what they see.
Also note you are only making money when you are on the clock, when you own a business you can make money in your sleep, have others making money for you, along with dramatically increasing your free time to your like while still making money. Your free time will become more valuable to you as you age, start a family, buy a home, etc. If you want more free time you will have to be in a position where you control the bulk of your time.