Python / Django developer
Aspiring rustacean
A VPN would be my first choice. ZeroTier works like a charm on the RPis. I’ve shared even SQLite databases over Samba over Zerotier among a bunch of RPis daily for a couple of years without a hitch.
TalkPython episode about Memray: https://talkpython.fm/episodes/show/425/memray-the-endgame-python-memory-profiler
PyQT / PySide are huge, but they have been very good in my experience coding cross platform desktop programs. macOS, Windows and Linux (even on ARM) are very well supported.
I’ve been following this project for a while and it’s great. They are just not great at promoting it.
Python / FastAPI will be better than Java in your situation and is easy to learn. Go should be even better and is also relatively easy to learn!