[BenjieGillam]

PostGraphile is designed for a situation where Postgres is your main data store, and other things are ancilliary. You can add in the other things with traditional GraphQL resolvers via the plugins/etc that you've mentioned; but if your stack is already quite complex with a lot of data stores that interact in interesting ways (i.e. not just driven by postgres and then fetching additional things from other stores as needed; but instead getting some from one, feeding it to another, feeding it back to the first, etc) you might be better off rolling your own GraphQL API that can handle your complex requirements.

If you like the plugin system, lookahead, etc then you could dive straight into Graphile Engine (which is agnostic to data store(s)) and use that to build your GraphQL API. If autogeneration and applying wide-ranging transforms appeals to you, that might be an interesting approach, but otherwise that system is not sufficiently optimised (yet) for one-off APIs currently (and is under-documented), so you might have a better time just writing your own types and resolvers with Apollo Server or similar.