Building a SAAS product was never simple. Now you can partner up with a Full Stack Developer to bring your idea to life. There is no need to hire multiple developers & designers to make it happen. A single full stack developer can do wonders now. Web application development process with a Full Stack Developer be like:
Picture worth a thousand words. Wireframes serve this purpose. If you have brilliant idea in mind and nothing on paper, you will face difficulty visualizing the solution be it web app or mobile app. Wireframing will bring the developer and product owner to same page regarding the expectations of the final solution.
Once the wireframes are finalized and overall flow has been established, it's time for UI/UX design of the solution (web or mobile app). User Experience (UX) provides the maximum user satisfaction when they interact with the application. User Interface (UI) provides the best presentation and interactivity of the web or mobile app.
Unit tests and integration testing can be performed with Jest and Cypress. Each library has its own pros and cons depending upon the type of application being developed. Sometimes this can be delayed and rather release for initial set of users who can provide feedback for improvements and report the bugs if found.
Heroku, AWS amplify, Netlify can be used as they provide free tiers for evaluation and charge you as you go. In case of mobile apps, these can be submitted to Google Play Store and Apple App Store.