The team size of the development team and its composition should be defined following the peculiarities of your solution and the needs of your project.
Moreover, such factors as your budget and deadlines also will have an impact. Typically, a SaaS development team includes a frontend developer, backend developer, UI/UX designer, QA specialist, and a project manager. Nevertheless, more complex solutions require the efforts of a more considerable number of specialists. If you do not have a clear understanding of the necessary team composition, you can get a consultation at a B2C or B2B SaaS applications development company that you will work with.