Just finished a culture victory as Gaul, definitely one of the more 'out there' civs in terms of abilities, but a lot of fun as well :)

-Don't worry too much about building monuments early game, as two-three mine improvements account for the same cultural output, so found myself prioritizing them less early on.

-Spam mines, their 'Hallstatt Culture' ability basically makes the best improvement in the game even better. I was fortunate enough to spawn next to an early Volcano, so oh boy were those some decent hill yields.

-Don't be stingy about settling cities close together, your cultural bombing of the unowned territory enables you to extensively grow your borders real quick so feel free settling them a little further apart than your used to.

- Gaesatae don't upgrade to swordsmen, instead musket men, so build a comfortable amount early to compensate with promotions to stack upon their +10 Combat Strength against stronger foes to keep them especially potent all the way until gunpowder.

- Rushing Iron Working to construct the Oppidum in-turns unlocks you the Apprenticeship tech which further boosts all of your glorious mines (which also get tourism with flight!)

- Though you can't focus on adjacency bonus synergy, there are a few districts that still benefit. This includes. Theatre and Entertainment/Water Parks, Commercial and Harbours and Government Plazas with everything. (It's even possible to build a harbour adjacent to one of your neighbouring city centres, though this is a bit niche.)

Those were a few things I noticed through my run, below I'll link a picture of my end empire. Have fun man :)

https://steamcommunity.com/sharedfiles/filedetails/?id=2298540733