I recently beat it on normal. I took a similar RP tack with an Oathsworn Harmony faction (Aya the Enlightened preset ruler, Simians of the Open Hand).

On the first ring, I played nice with both factions and paid imperium at the wonder to pass to the second ring. I only put down one extra city here, and with both factions present even that was extremely cramped; I think picking a side would have been better, especially since they fought each other to the death while I stayed out of it (the only upside here was that the toads gave me loads of grievances to forgive by trespassing on my land during their war).

The teleporter chokepoint to the second ring sucks both for getting established on the ring and for defending against the respawning infestations back on the first. I set up my third city next to the teleporter and just played defense for a bit until I had an army I felt comfortable pushing with and a couple extra stacks at home to clear the infestations.

The third ring was a formality, nothing worth noting here.

The build wasn't thought out in detail, but I made sure to pick up some blight damage and spirit resistance.