I purchased this game about a year ago, but just started playing it along with the Wake of the Herald expansion a few days ago. With so many options in terms of galaxy sizes and AI opponents, I'm curious whether there is a consensus as to a good set of options.

I played and lost using the 60-system spiral galaxy with Terrakin vs. 2 computers a few times. After that I played a 30-system spiral galaxy with Terrakin vs. 2 computers on easy and won. I then started a 120-system spiral with about 8 computers, and am winning but it's getting a little boring to slowly march across the galaxy capturing planets.

Since my original post I've played the "Expanse" map where the galaxy is limitless. AFAICT a few systems are generated whenever you colonize the edge of the galaxy. The feel of the game is completely different because the Remnant forces are so much stronger than in the spiral galaxy. The game almost becomes a puzzle where you see how you can slip past enough of them to get your planets leveled up.

I'll probably go back to playing on spiral galaxies for awhile.

I'm finding i prefer a more spaced out galaxy formation over the default 6500, something in the range of 18000-20000. Added to that in the 'Game Options' for galaxy creation i increase 'system size' to max (300%) and increase 'planet frequency' to about 200%.

This is for a 150-200 Systems single spiral galaxy with all the races.

I'm not 100% sure i have hit the right setup yet (maybe another galaxy or two could be an option?) but i certainly found the default setup and easy access to FTL like movement made the game feel pretty small and easy to cover the vast distances very quickly.

try team play on two maps... you + race against computer races

Good idea (the team play option). I think as i get used to the game and build up the difficulty level, that could be a great option.

Currently i have settled on this setup:

Myself vs all other races (so 8 races). difficulty Easy (while i learn the game).

Galaxy type: Clusters (these have z-depth! where the Spiral Galaxies are flat) x2 (so two such galaxies)
Systems: 150-200
Spacing: 13000

Game Options (those not listed are at default settings):

Planet Frequency = 250%
Minerals/Ore Asteroids = 60%
Resource Scarcity = 150% (this will give us some empty planets per system)
System Size = 300%

Enable Dread Pirate
Diable Starting Fleets
Enable Terraforming
Remnant Aggression

All others are 'unticked' the enable diplomacy events also (as i find they spam the main UI too much even if i have no contact with other races.

Enable Dread Pirate = why?

Why not?

Extra challenge, and and extra random event that keeps you on your toes. You need to be in the titan area of the research tree to have a counter to just how powerful the Dread Pirate is, but i imagine it would be good XP for the ship/fleet that takes it down?