How to choose which stack? [closed]

I am developing a website that will handle registration. I built a prototype using Python and Flask and bootstrap templates however I found that it wasn't as scalable as I needed. For example to add a new input field it would require several changes to several files to get it all to work.

In simple terms I am looking for advice for a combination of stack/language/framework to achieve the following:

1. Design a registration website (perform some moderate background tasks)
2. Simple login system
3. Easily interfaced with a database (preferably MYSQL)
4. Easily generate PDFs from data from the database
5. Send emails
6. Scalable UI (Easy to add input fields and easy to interface inputs with database)
7. Easily add new pages/routes

Any advice on a combination of stack/language/framework would be appreciated.