The OP is trying to run a mixed analytic workload which Postgres does poorly even at relatively small scales. No amount of "light tweaking" can fix it, it is intrinsic to the architecture. You can put 100B records in a Postgres table (I have) and it works if your workload is trivial but not well. The Postgres internals are not designed for data this large, it is an OLTP system.

You can do fast-twitch analytical queries (sub-second, a few seconds at the tail) on complex operational data models where you are inserting millions of records per second on 100B record tables while those queries are running. Just not on Postgres.