I dont know if I understand ok!

For the fastapi server? just use a cheap vps server or a CNAME on your domain to a VM in your home/office. For just deploying APK I would suggest just sign the apk with b4a and manually install from a fastapi route (is all free) and if you need more security, just add a wireguard layer for VPN. Anyway... what do you call a medium organization? Because for a fastapi server + mysql + VPN maybe is not the best architecture (surely is not)... I dont know what kind of app and data we are talking about!

I dont know if we are talking about a 'neighbour community' app, a multiplayer game, or an erp based app for 100 employees!!
Anyway, nowadays all the backend can be made by the LLM too... I use CC to implement complex integrations in multiple servers at the same time via SSH/WinRM and works like a charm (just ALWAYS make a plan, and ALWAYS review and check the results... fails little, but fails).