business method patents for fintech startups

Business methods can be patented so long as the "invention" involves more than some abstract idea thinly veiled as being accomplished on a computer. Whether your particular technology is patentable is a question whether it is (i) patentable subject matter, in light of statutory requirements and recent case law (e.g., Alice Corp) and (ii) sufficiently novel and non-obvious over the prior art.

Source code can be (thinly) protected under copyright, but generally your ability to stop someone from "doing" what you are attempting to do is to have patent rights to just that. A reasonable first step would be to speak in private with a patent attorney who can render an opinion on the patentability of your technology prior to pursuing what could be a costly, even if unsuccessful, patent prosecution.