Haven't found much time to report but here's finally some. A lot of things are going, the game is heating up... it's T85 already. Some pics are as old as T78.
First some "news from empire" then maybe some plans/tactics in the end. Okay here we go.
Scouting Dave/xist borders.
Grabbing some bears for extra culture + happiness.
Flawless win.
I found something odd with (+10% from TRs with Foreign Trade).
Notice the city has +300% in total (so should make 3c) but for some reason the bonus from FT is counted AFTER the other bonuses and it rounds down. 1c * 2,9 = 2,9 ~ rounds to 2. After that 2c * 1,1 = 2,2 ~ rounds down. I don't know if this is intentional (feels unlikely?) but the TR bonus from FT is totally useless (unless you have 10c trade routes...). I don't know if this was a known bug/mistake but I only noticed it now.
T81 Brian built The White Hand.
Need to be careful so I will strengthen Edoras. It's not easy to capture even with PoWs. I hope he forgets to use his WS

.
Notice I also found OO (for Cultists). More on that later.
Bree has been founded.
It'll grab Pearls (happiness + extra commerce from Jeweler) and also added +3c to mainland trade routes.
Coldrain built Barnaxus and killed it (on purpose) next turn.
The plans is obviously to build Shrine of the Champion for extra promotion to his Mages.
Dave is exploring the Ship Wreck next to my border. Not very happy with this...
... and the result.
Ehh... Well, not the worst to be honest. At least Dave didn't get anything good from it and this isn't as bad for me as it could be (Azer or Stygian Guard would be very annoying). I should be able to kill these quite easily (not the Serpent though). It can act as a guard for me in case Dave has any plans to attack with boats later. That's the thing I'm probably most worried about in the long-term when thinking about Rivendell. That's where the Cultists should help me.
Some got Great Sage. It could be Dave to bulb his magical route or then it's xist.
Next settlement will grab the gold (3rd Jeweler resource). Probably will settle on Copper.
I also discovered something really nice this turn.
See something? I am making some cash, culture and hammers just with citizen. I am in Caste System but I didn't realize that it applies to Citizen also. I guess they can be called "specialists" also.
You might notice I haven't quite followed the initial tech plan considering Culture Victory. Well, the thing is my opponents can tech to Mages fairly soon ~20 turns and I need to be prepared. I am vulnerable to some galley invasions from Dave/xist. On land it should be pretty slow to get to me and my land is mostly AF making it even slower. Still need to find coldrain, to my east it should be... hopefully far away.
I should consider burning the port cities to the inland sea. With Cultists this could be done fairly easily.
The problem is I don't want to make myself a target or get an angry neighbour just yet. I could also put Triremes in critical spots to guard against potential naval invasion in the future. The island will always be lightly defended but Rivendell must be very well defended. Don't get me wrong, the attack from Dave won't come too soon. But once he gets to Mages (about 20 turns maybe?) it'll be thing I need to consider. I am leaning towards not being aggressive but I'll grab Animal Handling for Hawks. Then I can scout enemy lands and see the incoming attacks.
I am still debating with "where to go next" in the tech tree. So many great options and hard to say when I really want to push that Culture path towards Mercantilism.
Demos as of T85.
Clear lead in GNP (71 of that is culture). That 27 GNP (Brain & Bing) is not looking very good

. My production is pretty low but Heroic Epic is making sure that in reality it's a bit more.