Replying to myself for now on the second point: I don’t see any way to configure the URL format, but after visiting several micro.blog sites, it looks like everything is using the /YEAR/MONTH/DAY/SLUG.html format, so I can probably get interlinking to work by stripping /blog and adding .html at the end across all my markdown files.
For tags, it seems like this will be converted to categories and will therefore go to /categories/CATEGORY/, so I can do something similar.
How would I handle redirections from the old URLs to the new ones though? It’s not like I can drop a .htaccess or nginx config file anywhere? (the existing redirection support doesn’t seem to cover this)