There was a guy on GitHub that added a Lemmy comment section to his blog hosted on his website. So it's already an accepted although niche usecase.
I feel like a single user instance of Pleroma would be more appropriate (and easier to host) but even though the character limit can be increased the remote limit of other instances might reduce your visibility, I am not sure.
Go by elimination, the first thing I would do is reset the phone and don't pair it to any bluetooth device. Also change the WiFi password and the router admin password with strong randomly generated passwords.
Then keep going as usual and see if something changes.
When you said you used a bug detector, was it a radio frequency analizer? Did you check while doing a phone call, a bug that is not transmitting wouldn't be detected.
Do the people you talk with or someone living with them know your neighbour? Maybe the leak is on the other end.
If the houses share an air conditioning system maybe try closing off the vents.
I know you are sure of your experiences but have you checked your physical and mental health? A few mental conditions could make coincidences turn into paranoia, but even a few simple physical conditions like carbon monoxide poisoning and maybe even vitamin deficiency could loosen your grip on reality . Has someone else witnessed first hand these events?
Why buy a project that is going to get abandoned and get a cut to Google? Wouldn't a direct donation and then buying the new app make more sense? Am I missing something?
A human should not try to answer it.