To put it as simply as possible. Try to stick to plain text as much as possible. Of course, let something like an SSG (Static Site Generator) handle the HTML conversion. Before you die, set/ask someone or an entity to host the HTML on a server that can host HTML (should be in 100+ years too).
As for the domain, keep renewing it a few years ahead whenever you remember. I’m sure there are registrars where you can add credit, and it auto-renews.
Personally (and I’m not sure and haven’t even started), I really liked owning and helping others own their digital assets online. So, I have been meaning to, or would really like to, start an Internet Business (registrar, hosting, email, forms, etc.). Thus, an entity that can live on after me, that does business while owning the current Internet Assets that I own now.