I built and run SugarWOD (https://www.sugarwod.com). SugarWOD is a workout solution for CrossFit gyms including apps (iOS/Android), website, plug-ins, and TV support. Was a solo, free service for the first 3 years. Converted to a paid model 1.5 yrs ago, and as of a few months ago have part-time contractors helping with tech/ops, mktg, and support.
I agree with novaleaf that a very broad skill set is needed, though I'd add that it might be enough to at least be interested in all the areas mentioned. You can learn a lot along the way, which is a big part of the fun. If you're focussed on making a great Product (capitalized product = the entire customer experience including everything from web copy, onboarding, support, performance, features, etc.) all of it is important.
As an aside, I think it is this breadth that allows someone to be a "10x problem solver", which to me is 10x more interesting than being a "10x developer". Code is a means to an end.
"Success" is a malleable and personal term, but by typical SaaS metrics SugarWOD is a success. Millions of workouts logged, paying customers, profitable, growing quickly.
More importantly, I get huge satisfaction working on something I feel passionate about, and I really love running the entire business from a laptop anywhere in the world (though I'm usually not far from Colorado :)