Finally got around to setting up a self-hosted mail server. In the end I went with Stalwart for it's Rust-y all-in-oneness and relatively simple configuration (including NixOS module).
It spat out the required DNS entries for SPF, DKIM and DMARC, I added them to my test domain with @beasts and carried out some tests with Fastmail, GMail and Outlook.
I checked the @aaisp IPs I'd picked hadn't made it on to any block lists.
And it just works! No issues with delivery so far.