Is it possible to run a successful company without being unethical or operating on the fringes of the law?
There is nothing inherently unethical about entrepreneurship. Find a problem people have. Figure out how much money solving it will save them (or help them make). Charge them less than that.
You certainly shouldn’t need to do anything illegal—in fact operating within the law is a requirement if you want your company to be successful, attract high quality customers and raise money from investors.
Plenty of people have built ethical companies. Some people take unethical shortcuts, but it certainly isn’t required.