Can an independent consultant/contractor become NetSuite Solution Provider/Alliance Partner? If so, how?

No. You need a minimum of 6 people in your practice.

Rules may have changed, but as far as I know (was a former SP), that there is not a minimum requirement; however, they would look more favorably if you were > 1 as they expect you to be able to have Sales resources and the ability to implement. There are quotas you need to uphold to stay in the SP program, and if you're not ready to sell NetSuite full time, it may not be the best fit for you. That being said, Alliance can be a better option if you're in the exclusive business of implementation and can do it well.