I had no idea how close the game was.
A few more reports, duh, all were done on Regent/Normal/3000 BC start
BURMA
Not much to be said, you have a crazy core and pretty straightforward UHV (build the Paya, set the slider to 0%, get a GM, hope for Chinese to collapse to get Iron for bombards, conquer Indochina, and at this point you are pretty much a great power; adjust sliders to get more GPs, i ended the game with 2 extra gold ages, mostly because China built Eiffel Tower in Yunnan and collapsed from sheer ahistorical aneyrism). I must admit that my fears regarding SEA being overcrowded turned out to be at least partically true, both Burma and Vietnam have claustraphobic (yet rich in resources) cores. Also, the horse source near Pagan is covered in jungles (so no pastures there before Microbiology) yet obviously is set to let Burma use it's second cavalry UU.
CELTS
How could one describe the Celts? Jolly redheads who like to dance and drink ale? A sophisticated culture without writing that never got a chance to shine by its neighbours? A reclusive yet hospitable people of early Christians?
Perhaps. But not in RFC DOC.
In RFC DOC the Celts are what the Chaos from Warhammer aspires to be.
Culture? Buildings? Technologies? Who needs all this trash, weak southern peoples? You are here to bring the Word of the incoming Apocalypse - and the Apocalypse itself. The only techs you need are Bloomery to make your Dark Green Crusade easier (on the second thought probably you don't need even Swordsmen, Oathsworn are only a bit worse at city assaults but cheaper and more mobile) and Priesthood to spread the Word.
Building pastures and orchards? Perhaps later, to celebrate our victories, when meat and blood of fallen enemies shall be in a short supply. Until then, chop the trees. Chop greedely and recklessly, there are no Ents (afaik). And build Oathsworn, hordes of them. Economy? Who needs it when you are about to bring the entire civilized world to its broken knees? When the Romans get conquerors against Greece, make your own move. Italy is usually lightly defended, and Swordsmen with Combat 1 + Shock are more than up to the task of facing the Legions. Keep building more swordsmen (and don't forget 2 Settlers and a Galley to settle in the north, closer to the Dark Celtic Gods; as a side note, Scotland is marked as the Rise of England area yet doesn't flip). Keep sacking settlements to keep your economy afloat. Once Rome is gone visit Greece, then Carthage, then whoever you want - upon French spawn your mantle of the ultimate evil will be passed to them and you will collapse to the barren core of Scotland and Ireland, so don't bother too much with stability and economy. At some point Orthodoxy shall begin to spread - you have no realistic chance to found it, even in the ruined world you have created (in my game Ethiopia founded it by being the last civilization (among with Nubia) with cities in possible Orthodox spawn zone), instead arrange massive sacrifices to the New God by whipping His monasteries and make His Anointed Missionaries (don't forget to celebrate their anointments with more whipping) follow your troops on their trail of destruction, preaching to the few survivors left among ruins of the old world. Probably you won't have time to finish your ritual of 12 preachings before the French appear, in this case you'd better stick to Orthodoxy if possible, get OBs with England and Vikings and spam Orthodoxy preaching in their cities (since they will likely be Catholics, Orthodoxy will slowly disappear from their cities, and UHV3 doesn't check if you spread to different cities; probably even more trollastic way to achieve this would be Religious Persecutor + the other Christian denomination missionary combo... should you be able to get at least to the Middle Ages by 1000 AD, let alone Theology). There is also a small mistake in the UHV description: it's stated that you have to spread Christianity 12 times BY 1000 AD, but it checks if you have spread enough times IN 1000 AD (despite there is no way to lose the counter). I used this small bug to spread the Cult of the New God 13 times instead, which felt more appropriate.
As a side note - never used Celtic UP, save for healing before taking Carthage - which would fall either way. It's definitely one of the worst UPs in the game, being both boring and not particulary useful.