Whatever framework and lang you have grip on, unless you want to learn some new technology.
Mostly performance bottleneck comes at storage level so go with better database as per your need and use hybrid approach, I.e choose SQL and No-Sql wisely as per your need.
If you want to learn the consider micro services, and choose any language or framework you like
Keep your API's 100% indenpendent and loosely coupled and avoid Session based authentication and use Token mechanism like JWT.
For frontend it's always good to use some binding framework like React, Angular, all are good and you can choose on your liking.
For saving\serving media use cloud services e.g Cloud Front, or Google Cloud storage etc don't try to serve from your Code instance.
Don't try to re-invent wheel So any language you choose always use a framework and follow its practices, don't try to do custom stuff unless you really need.