For (1), I added a sentence about using DATABASE_ROUTERS to avoid any queries to the default database if you want to run without one.
For (2), I added a similar sentence about using routers to avoid creating tables where you don't want them, but avoided any specific recommendation as I think it's best to let users figure out what tables they want and where.
For (3), after further investigation, migrate does support the --database flag and as far as I could tell the documentation is accurate with respect to how it works.
Note that for apps with migrations sqlall is replaced by sqlmigrate. Given the complexity of migrations, it seems like a bad idea to recommend that as a "fine-grained" approach the way sqlall was, so I removed that suggestion.
Feedback on the patch is welcome.