Can I start an ordered list at a number other than 1?

Yes — the number of the first item is respected by the renderer. Writing 5. as the first item starts numbering at 5.

How deeply can I nest lists?

There is no hard limit in the Markdown spec, but past 3-4 levels readability suffers. Most renderers handle 5-6 levels gracefully.

Why are my task list checkboxes not rendering?

Task lists are a GitHub Flavored Markdown extension. Make sure your renderer enables GFM — ours does by default. Also note that the syntax requires a space inside the brackets: - [ ] and - [x] (with a lowercase x).

Do nested ordered lists number correctly in Word?

Yes. The converter writes the number as literal text (1. 1.1. 1.1.1.) so nesting is preserved and each list still restarts cleanly. Earlier versions had a bug where lists shared numbering state — that has been fixed.