I've updated the tech trees above to indicate with an asterisk the techs I'm looking to flavour. I would love to make all 31 civs have a unique gameplay; or at least have a gameplay that is different from most, though sharing with one or two other civs (like the Huns and Scythia): 31 different methods is the aim though, but it's a big undertaking!! However, as you'll see below, I've already got ideas about 21 of them - though Etrusca needs more adding to it and I would like the Huns and Scythia to differ in some way if possible.
Please make suggestions in the direction the civs should take; I've listed below the 31 civs in the mod, plus some notes with the ones I've already made some decisions upon. Naturally, through doing this, the mod may become a little unbalanced - we'll all have to play the darned thing to discover by how much!! Whilst I don't normally like to be "pulled" about historical accuracy, citing gameplay as more important, please feel free to do so here, as I might not be accurate in my assumptions below:
01. Anglo-Saxons : era three unit boost : all era three units recieve +1 HP. Tafl house is an era three flavour +1 happy face improvement building; Legend of Beowulf in early era four grants a free Saxon infantry every five turns, which doesn't expire. Treaty of Wedmore in era two grants a war weariness reduction in all cities.
02. Armenia
03. Arverni : agriculture : can irrigate without access to fresh water once irrigation has been discovered (other civs wait until plumbing in era two). Wonder in era one grants free granary in every city, whilst era two wonder grants "city growth causes +2 citizens instead of +1". Possible unique access to extra food resource from era two.
04. Athens : seafaring and scientific bonuses: seafaring in era one - access to Great Lighthouse grants +1 for all ships and safe sea travel. Access to three academies in era two all doubling research in the city. Also, they have the "philosopher" citizen instead of the scientist; they're better than the scientist, but not quite as good as the Persian Magi. (Please note that I'm not saying that they weren't as good historically, just making things better balanced in terms of the mod).
05. Axum
06. Carthage : trade : bonus luxury item available from the start; Carthage can also trade maps from the start. Double harbour in era two gives free veteran galley every 5 turns - even if it's built before galleys can be built independantly. Wonder in era one allows safe sea travel and +1 to all ships.
07. Celtiberians
08. Corinth : Trade benefits : Era one - Temple of Apollo wonder (+1 trade in every trade producing square); era two - Isthmian Pottery trade wonder (bazaar in every city on continent); era three - Isthmian games wonder (flavour +1 happiness in every city); era four - agora improvement +50% tax output. However, no war weariness reducing buildings.
09. Coritani : Archery benefits: Era one : no barracks available, but can build archery range improvement, which is a free barracks. No Milon of Kroton available though. Era three : Volisios' Archery range wonder - provides free Coritani archer (their UU) every 5 turns. All archery units have stealth attack and +1 HP. Druidism in era two.
10. Dacia : diplomacy : the Dacians have diplomats enable from the start; they can also negotiate right of passage and trade communications from the start as well. A wonder in era one grants a free courthouse in every city - which doesn't expire.
11. Egypt : builders : access to Egyptian builder citizen from the start; can build the Pyramids in era one for free granary in every city and the Sphinx in era two for war weariness reduction in all cities. Temple of Karnak flavour wonder in era three doubles the effect of temples. The senet house improvement in era four gives +50% luxury output. Plenty of flavour buildings to throw in as a culture group on its own.
12. Eire : culture bonuses : extra improvements with no maintainance purely to boost the culture levels; Newgrange wonder builds such an improvement in every city in era one; Book of Kells in era four again builds such an improvement, but also this improvement (unbuildable without the wonder) adds +1 happy citizen. Druidism in era two.
13. Etrusca : pottery trade : wonder allowing free pottery shop in every city in era one (whether there's clay in the city radius or not).
14. Huns : nomadic : Wonder in era two allows free leader every ten turns; their settlers are on horseback, have a defense value (maybe 2?) and can move 2 spaces per turn; all their horse units have +1 hit point and are unimpeded by terrain. They are able to build stables instead of barracks in era one, and these are free of maintainance fees and build veteran ground units. However, they receive the aqueduct and hospital improvements (which increase city size) later than other civs.
15. Iceni : chariotry : Boudicca's revolt wonder in era two allows Iceni chariot (which is their UU) to be built every 5 turns. All chariots have +1 HP (including early chariot in era one, which is -1 HP for everyone else). Icknield Way wonder in era three is a flavour wonder adding +1 happy citizen in all cities. I might also (for flavour) give them an extra chariot unit in era three instead of a horse unit, but values remain the same. Druidism in era two.
16. Illyria : piracy : Teuta's dockyard wonder in era two produces a free pirate ship every 5 turns, which has hidden nationality. Couple this with the fact that her flavour units (including her UU) have amphibious attack and you have one heck of a treat when it comes to sneaking up on coastal cities.
17. Iona : druidism : the druids of Iona can build the druidic altar for extra culture in era one, but this also doubles sacrifice. They're the only civ who can boost their culture rating in this way. St. John's cross in era two builds a free burial mound in all cities; in era three they have St Columba's Monastery wonder - which gives them an extra monastery (+5 happiness); Iona abbey, in era four, doubles the effect of churches.
18. Jutes : land workers : workers work at double the rate of normal workers. Era three gives bonus improvement to boost shields in water.
19. Kushan : multiculturalism : access to forms of government which allow 100% assimilation chance as well as being as good as the best contemporary government; building allowing city size two in era one and city size three in era two - faster than other civs. Era two allows wonder giving "city growth causes +2 citizens instead of +1". Era three has happiness improvement/wonder to keep their booming populations in check. Era four has wonder giving +1 trade in all trade-producing tiles to reflect their commerce with Rome.
20. Macedonia
21. Marcomanni
22. Nabataea
23. Ostrogoths
24. Parthia
25. Persia : Science : access to Magi citizen instead of the scientist; Magi are twice as effective; +2 free advances wonder in era three; wonder in era two gives a free school in every city. Wonder in era one reduces war weariness in all cities; this replaces a war weariness reducing improvement civs normally get in era two.
26. Picts
27. Rome : organised : unique access to the Roman prefect (equivalent to the policeman in the "epic" game). Barbers in era three give +1 happiness (flavour improvement), but require the hospital to be built, so it's only available to size three cities. Temple to Venus in era one reduces war weariness in all cities; temple to Mars in era two allows the Romans to build larger armies.
28. Scythia : nomadic : as per the Huns, but I'm looking for a unique difference within this.
29. Sparta : Hoplite force : Spartans have maintainance-free barracks from era one, which also have the additional side-effect of reducing war weariness in the city. The Spartan Agoge wonder in era two produces a free Spartan Hoplite every five turns, even if you haven't discovered armour, which allows you to build them. The era two defensive units have +1 HP and don't require iron.
30. Thrace : Mercenaries/slave revolt : Their unique unit, the Thracian mercenary, available in era two, as well as being a good unit to have, can be sold in negotiations (it'll have the old worker slot

); Sparticus' slave revolt allows free worker housing in all cities in era three. Any slave markets built in Thracia are automatically replaced with these. I might shift worker housing for other civs to Feudalism in era four, thus leaving slave markets in effect for longer. Incidentally, for those not in the "know," both slave markets and working housing increase productivity, but slave markets (available with slave trade in era two) add 2 unhappy citizens. They have the "replaces building with this flag checked" ability). Slave markets are unable to be built after urbanism.
31. Visigoths