One thing, I assume you thought of this already: is it ok that a single upX.sql contains all those UPDATE and ALTER TABLE statements?

It is - there should be "at most one schema-modifying statement" - aka 'DDL' - (the ALTER TABLE) but any number of "data modifying statements" - aka 'DML' - (the UPDATE statements).

It's not visible, but we're implicitly doing extra DML statements within each transaction too, to help verify the database version is correct, and to prevent us from applying old updates.

Also as of #9878 we actually have automated tests verifying that each transaction has "at most one" DDL statement

🚀