To help propel people, I will itemize MY preferences:
MariaDB (sql is fiiiiine and maria is free from oracle machinations.) I'd also happily explore Neo4j, but am not comfortable enough to actually recommend it outright.
Redis seems obvious to me, here.
I suggest service oriented and docker/kubernetes facilitated and deployable by anyone who wants to run a local/regional node for a few bucks a month off anything like openshift or heroku or aws or azure whatever they want. Scale by free distribution and collaborative standards rather than centralized expense.
I'm happy with REST and GRPC
OAuth?
If it were just me on my own, I'd use perl's mojolicious. I ASSUME most folk in this group would prefer django or flask, which I'm not interested in fighting about.
Not a VERY strong decision... presumably angular or react.