I have written scrapers for several websites throughout my career including ridesharing sites, job portals and classified ad sites. Most recently I have worked for a company that extracted information from real estate portals, for which I have also designed a program that checks whether the scrapers are still working correctly, which is a perpetual concern with scrapers, even if you have enough experience to know what way you can build the most stable scraper.
If you are looking to build a website and a mobile app, it probably makes sense to write an API (the back-end) that can then serve requests from a web app, mobile apps and any other app you might want to build in the future. A RESTful, JSON API was what worked best for the companies I worked for in the past, and what I am well-experienced with.
There are lots of options for building the user-facing apps (the front-end), but it might be beneficial to look at React for the web app and React Native for the mobile app, since you might even be able to share some code that way. While I have already collected experience in working with React and React Native and would love to get my hands on it again, I’d also like to point out, that splitting your system strictly into front- and back-end, as I proposed above, makes it easy to develop the front-end app and back-end app in parallel, meaning you could go live faster. So that’s also worth a thought.
Let me know if you have any further questions, I'm happy to help!