For some of the simpler sites sqlite would have been fine, but I do need Postgres anyway for some other stuff on my server so the overall burden of standardizing on Postgres only is less than having to do tuning for two different databases. In particular sqlite has worse defaults due to backwards compatibility, so you have to do a lot of upfront config for every table and DB.
Postgres version upgrades are basically painless, at my workplace our upgrades complete in so little time our users don't notice, and we have more data than probably 99.9999% of companies out there (mature company in aerospace industry).
Well if you already have Postgres then yes, sounds fine. I don't really agree that SQLite needs tons of tweaking -- setting journal_mode to WAL/WAL2 is the only real thing worth doing, everything else I would consider optional.
Version upgrades for SQLite are basically a no-op though, that's kinda one of the reasons why it's so great to run in production (and deployment a maintenance being mostly a no-op as well, apart from setting up backups I guess).
I don't actually suggest that everyone should run their production on SQLite, but it's genuinely worth considering especially for small-ish projects.
Foreign key constraints, sync frequency, busy timeout, strict typing on tables, explicit types for integer primary keys, and a convention for storing dates and times are others I would want to do up front.
I set it to enforce foreign key constraint as well.