They are a bit all over the place - I started this years ago so I don't really have anything solid, but searching gives a few results that looks pretty solid ([1] [2]). If you temporarily tried doom [3], I think you could see how it would work for you. You need to install something like isync as well so you have a mailbox index locally. I would start with just one account - multiple accounts is a bit more effort.
In general, be prepared to spend some time getting this to work. I wrote a bunch of elisp, but you don't have to write much. For me it was worth it, but this is not a plug-and-play solution unfortunately (nor is notmuch).
Thank you. After I posted I realised my stupidity in not checking
out your linked config file. Having fun with that now. Cheers for
the additional nfo.