More than one server. Sqlite should be thread safe and simple services can scale to thousands of parallal users. If you are OK with some downtime every 6 months when server goes down it will scale well. Deploy/ rollback will be an effort.
To keep this simple, I'm thinking exporting just the necessary data from each db and inserting that to a stats db (having a source column to each table, referring to the original db). Then load the stats db with Metabase or something.
Migrations on the stats db may be a bit of a pain, as well as making sure that all data is exported and imported correctly every time.
I'm sure there are better ideas.