Postgres makes a lot of sense with append only tables. You can easily partition them by time (usually) and thus have an easy way to break up the index trees as well as using a cheap indexing scheme like BRIN and being able to just drop old chunks as they become irrelevant.
Solid seems awesome. Though as a Svelte dev, the jsx / React flavored api felt like a regression from the simplicity and readability of Svelte’s template syntax. Have you explored both in depth? I’d be curious to know Solid and its ecosystem compared to Svelte and Sveltekit .
Of course you can throw more servers/caching/database locks, but the advantage of using Elixir & Phoenix is that you can do a lot more with less.
Think how much the code would be simpler and easier to reason about without caching.
Or reducing the numbers of servers you need from 150 to 2 and with better performance [1]
If I had to use OpenAI API I would pick my favorite HTTP client and just use the Rest API and write a small wrapper around it for my needs.