Help, my POC got funded, need serious Dev advice to build and scale my Flask app

I am new to full stack programming and 6 months ago I started building a proof of concept web app, it worked well enough for a company to acquire me. I now need serious advice / consulting on how to make it properly so it will scale. So far it's a Flask app on Google App Engine, with PostgreSQL database and totally vanilla frontend. About 5,000 lines of code, but might make sense to re-write it now before hiring more devs? Basically, I was advised to pay a lot for a good senior dev to structure my app properly now over the next month as a freelancer / consultant, before I actually start hiring people. What do you think? Anyone here good enough or interested enough to help a fledgling startup ? Regards, James