

TBH, it sounds like you have nothing to worry about then! Open ports aren’t really an issue in-and-on itself, they are problematic because the software listening on them might be vulnerable, and the (standard-) ports can provide knowledge about the nature pf the application, making it easier to target specific software with an exploit.
Since a bot has no way of finding out what services you are running, they could only attack caddy - which I’d put down as a negligible danger.
You will simply not be able to install anything, unless the FOSS dev is cool with providing their ID to Google, and agrees to its ToS, and Google likes the app and signs it.
Which many devs (myself included) will definitely NOT be.