For holding (HODL) I’d recommend Anonero. The site is only reachable through tor (anonero.io). And technically it’s two apps. Anon (for your offline-only device) and Nero (for your everyday/online phone). The spend keys are stored only on Anon. Nero has only view keys. If you want to do a transaction, you need to scan QR codes with the devices a few time to transfer information and the signed transaction.

For everyday use probably cake wallet.

Interesting, thanks for sharing!

Oh the idea sounds very nice! Does that work like a captcha? How would I integrate this into a site?

I would say yes. You download the app (playstore, appstore or fdroid), install it. Then on first time opening it you need to choose a pin for the app and an username for your first profile. Then you can start chating. The gui is pretty similar to signal. And it works pretty good so far. I had problems with calls last time I tried (but a few month back it worked).