I don't know a good template, but whatever you choose make sure it uses Markdown for the post format. Markdown was originally designed for exactly your use case. The Daring Fireball blog has been using Markdown for 20 years now.

There are variants of markdown, and I'd go with Github Flavoured Markdown which has all the features you require and has quite a few improvements over the original spec:

• Basic GFM tutorial
• Full GFM spec

For the few things it can't do, like embedding graphs — Markdown is a superset of HTML, meaning that arbitrary HTML is valid Markdown. You could, for example, use D3.js.

Personally I would also use GitHub as my distribution method. Write your posts in any text editor, push to GitHub, and then a GitHub action triggers an action that re-generates the HTML and publishes your site.

That approach will work well and if it ever stops working well you can easily move part of your system to something else without reinventing the entire thing.