I don't have any suggestions but would like to give my thanks for the quality content

$0.14 per user per month is... Higher than I expected.

Yes it's FOSS: https://github.com/dessalines/jerboa/blob/main/LICENSE

Unsure on the rest

Bingo. Same with Beehaw and many others.

0.18 was a big change (for example websockets to http), I'd imagine future versions are unlikely to be so drastic and will allow Jerboa to be compatible with older versions

I've been considering getting one but I've read too many horror stories about them breaking