For a side project? I'd start by creating the store API I want so I could swap storage backends later. Then I'd use PostgreSQL with PostGIS. Fastest way to get

For a side project? I'd start by creating the store API I want so I could swap storage backends later. Then I'd use PostgreSQL with PostGIS. Fastest way to get up and running and it will scale decently well. Well enough for a side project. If you get traction and scale takes off, switch to something more exotic. Until then, a single PostgreSQL instance will work wonders.