Now that I seem back into playing Civ4 mods, I decided to come up with this list to help you out iron out some errors along with some suggestions:
1) Horses were not introduced/used in India (South Asia in general), until the Ghorid/Mameluke dynasties introduced them into the continent in the early 13th century. Elephants were predominantly used before then.
2) You should add a pre-Mongol central Asian civ, I highly recommend the Yuezhi/Kushan. They were critical to the spread of Buddhism and contact between Gangetic civilizations and Northern China. They would also populate Central Asia with some cities, to make it less barren (post-300BC Central Asia became the main highway of inner-Asian trade). Frankly speaking if you have Tibet, I have no idea why you don't have a pre-Mongol central Asian civ. They could later become the Uzbeks in a later spawn, to threaten Iran.
3) China and India did not connect to each other through the Himalayas, there is no known passage way through the Assam region into China, until the modern era. Instead Central Asia was used as a passage way (read above suggestion).
4) Get rid of Shanghai as a potential city for China. Replace it with Nanjing or Suzhou. Shanghai, like "Tokyo", would not become important until the 20th century, before then it was a sleepy fishing village on the coast (no one built cities on the coast for good reason). Suzhou and Nanjing were far, far more important cities. Feel free to have them renamed to Shanghai later in the game, like Edo -> Tokyo, but frankly I don't think you need to, Shanghai only prospered as a European Treaty Port.
5) Bug: Persia declares war on India when they spawn, and then immediately makes peace.
6) India first name should be Mauryans, and then Medieval name Guptas.
7) Cotton should only appear in Iran with the arrival of Islam. Cotton was not grown in any significant quantities there before then. In fact the growth of Islam in Iran, is linked to the growth of Cotton in Iran (see sources). Generally speaking, the Iranian plateau had no major cities before the arrival of Islam, the Persian administration was always based in Iraq, never in Iran. It is only with the arrival of Islam that Iran became a major trade and commercial hub, directly linked as well with the growth of summer crops (such as cotton). All of this before the mini ice age in the 1000sAD, which sent Iran into decline.
8) Stop Babylonians from becoming Jewish.
9) Ideally (if possible) Babylonians should be like the Harappans, start early, die early. Then respawned as (unplayable) Assyrians.
10) Where are the Eastern and Western Ghats? Southern India (the extreme south) needs to be more mountainous. There is a very good reason that Southern India maintained naval Empires and its independence for so long, and its not because they ate chili pepper
11) Consider having Islam spread faster in the Cordoban civilization OR have them start with more missionaries. I'm seeing Catholic Cordoba (due to cities in North Africa) one too many times.
12) I truly understand the decision to make Camel Archers the UU of the Arabs, it is a very standard cliche, and for sure many Bedouins fought on camels. However by 300BC, Arabs were quickly becoming very rich (due to multiple reasons I won't get into here), to the point that they were building large well decorated cities (see Petra or Palmyra). Camels remained important (in fact they were critical), but in warfare it was the horse that dominated, even after the invention of the North Arabian Camel Saddle. Horses could now be bought and fought in battles, even if the Arabs took camels to the battlefield. I would strongly suggest you replace Camel Archers with a horse warrior. IMO I would replace them with Ghulam or Mameluke as heavy infantry. Make Knights keep a camel portrait as unique art. We can talk more about this if you want more details.
As for the bow they come with... have you ever tried to shoot a bow from a camel? Doesn't work... try lance instead (check SoI).
13) Arabs should be Tribalism NOT Slavery civic. Yes the Arabs practiced slavery, but NOT the slavery depicted in the game. Agricultural or labour slavery did not exist in any meaningful way except briefly in the Abbasid period, until that resulted in a short lived African servile kingdom in Southern Iraq.... ya.... that practice didn't last long. Instead they were kept as domestic slavery and as warrior elite, which is not depicted in the game. If anything the Arabs should be Agrarianism (when they get it).
14) I really like the idea of Buddhism growing out of Hinduism. Please consider the same for Daoism, or consider scrapping it all together. Its a "philosophy" which affected parts of China (not even as important as Hinduism -> South/South-East Asia), and even then compared to other religions you have added, I don't see its value. If you do keep it, have it as an outgrowth of Confucianism. Perhaps once you build one Confucian temple. In many ways Daoism is a rejection of Confucian thought, and it would be silly if it was found somewhere else (as happens sometimes in the game).
15) Considering that Venice gets conquered EVERY single game by either the Germans or French, lets just replace it with Milan. I understand that Venice was an important city-state, but frankly speaking this game can't do it justice (which is fine), instead let's just have a city which was actually contested by the HRE/French, not to mention its own independence (Italy civ). No point having a German Vendig every game, it just looks bad. Alternatively if you want to go crazy, add a Civ5 type no-settler Venice. Wouldn't even have to be playable!
16) Consider if possible separating Military access from having trade. Its awesome that the French/Germans/Poles trade with teh Ottoman Empire, but they don't need to give them military access to conquer Scandinavia. I can't imagine this would be that difficult to do either (please correct me if I'm wrong!)
17) Since the Spanish control Toledo (Madrid) at start, consider having them be spawned instead in 1085, when they actually seized the city. Before then they were minor regional players anyway, there is no real reason to have them as early as they are. Plus in 1085 they can be buffed a bit to make up for the later start.
18) Consider having Madrid only be named as such by the Renaissance. Before it should be Toledo. A la Edo -> Tokyo.
19) In my opinion: Ditch the Italians (until the mid-19th century), and add in unplayable, no-settler, non-expansionist Papacy. Have it be modelled off of RFC Europe Papacy. I'm not expecting this anytime soon, but as a long-term project this could be AWESOME to interact with.
20) Why does Spain start with Organized Religion and not Fanaticism like the Arabs apparently do? While it was the former who organized the wholesale removal of two religious groups (hundreds of thousands of people) and it was the latter who accepted religious minorities (INCLUDING Zoroastrianism) as a matter of law. If anything it should be the other way around. In fact I can't think of any civilizations that should have "Fanaticism" as a basis of their religious "civic". Can you?
21) Cordoban Horse archers make me laugh... please consider replacing horse archers with something else. Historically very few peoples actually used them. Make them a unique barb/Seljuk unit. No need for any other civ to use them. Make Horse Archers light cavalry or something.
22) Marseille is only Jewish? Why does it not spawn with Catholicism?
23) Constantinople should be the head of Orthodoxy. With the exception of the post-Ottoman era, the entire history of Orthodoxy has been dominated by the Patriarchate in Constantinople. In the 600AD start it is in Jerusalem for some reason... but Catholicism is not??
24) Does Orthodoxy spread to Russia? If not, consider having it do so by script, or have them start with Orthodoxy, and push up the start date on Russia. No point in showing pagan Russia starting off in Moscow instead of Kiev.
25) Beijing shouldn't be called "Beijing" until the modern era (a la Edo -> Tokyo). In the 600AD start call it Yan.
Note: Love all the QoL features, really great work on that (amongst many other things). Anyway this is my first 25 points, I'll work on the next 25.
Sources: There are quite a few sources I drew upon, and if you want a source for any specific one, just let me know. Here are the major ones though:
1) New Cambridge History of Islam
2) Dr. Richard Bulliet History of Iran to the Safavids (iTunesU)
3) Dr. Richard Bulliet World History (iTunesU/Youtube).
4) Imperial China 900-1800, F.W. Motte
5) The Camel and the Wheel, Richard Bulliet
6) The Making of Europe 900-1300, Robert Bartlett <-- As a German/European a must read. Key book in contemporary Medieval studies.
), but I'm saying that Jerusalem should not be the holy city for Orthodoxy, Constantinople should be. 
