A1:

This cannot be stated with any certainty. We can say that "it is believed that St. Thomas founded the Christian church" or similar statements. But it cannot be proved. There are no documents which show this.

Having said that, there are many church pamphlets and WP:POV histories which say this, but none are considered WP:RELY.

A2:

The only document we have suggested that he preached in "India." This name was given by Europeans who were not very familiar with geography beyond the Mid-east, to the area around the Indus River, or Pakistan today. It is not known what inhabitants of Kerala then called themselves, but it is unlikely they thought of themselves as "Indians" or a single group, since they were in a separate realm. Possibly by the time Marco Polo visited, the subcontinent was then known as "India" to Europeans.

There is better information that another Thomas did arrive in the 3rd century, was successful and later became conflated with the Apostle.

A3: Actually, St. Thomas has about 7 or 8 graves, mostly in India, but at least one in Antioch. There is no "proof" as we understand it, that any of them contain the remains of a first century human, much less St. Thomas. So the problem is not that he is not buried somewhere. The problem is that he is buried in far too many places! For many articles, we can say that "local people believe that he is buried here." His body is reported variously at 1) Urhai (modern Edessa, having been moved from India, 2)Ortona, Italy, 3) Mylapore, 4) a skeleton identified then as the apostle was excavated from Mylapore and brought to Portugal where it languishes (unrecognized), 5) a second excavation discovered new remains with a spearhead which relics are believed by the Indian Catholic community to be real, 5)

A4: We can say that "it is believed that St. Thomas in buried at x." This is not readily one answer in the article about St. Thomas, but that is a separate problem from the history of Indian Christianity

A5: Brahmins or (name) did not arrive in Kerala until x. Therefore Thomas could never have met them.

A6: This is against Wikipedia policy WP:MOS which states that honorifics must not be used in articles. Okay to use titles once, like "Archbishop" or "Catholicos," but not more than once per article.

A7: The Ten Lost Tribes were lost to Israel when the country was separated into two kingdoms. The northern one was defeated and the inhabitants killed. The "lucky" ones were carried off into slavery and concubinage. There were no "wandering" tribes. Nor did they escape or even try to. They stayed to defend their nation. Few survived.

A8:

The figures for membership, or for any other sensitive material, should be taken from reliable sources, outside the church itself or its adherents.

The best source of this demographic information would be the Malayala Manorama Year book (the most widely circulated year book in India). There is also the government website, http://censusindia.gov.in/Census_And_You/religion.aspx, which confirms the Kerala Christian population as 19% of total; a little over 6 million.

Here are the figures from the year book (rounded):

Total Christian Population in the Indian State of Kerala: 6.1 million:

• Roman(Latin) Catholics: 1.4 million
• Syro-Malabar Catholics: 2.2 million
• Syro-Malankara Catholics: 100,000
• Malankara Syriac(Jacobite) Orthodox and Malankara(Indian) Orthodox combined*: 1.4 million
• Marthoma Syrian Church: (340,000 to 1 million- currently under discussion)
• CSI: 380,000 (0.38 million)
• Other smaller protestant sects together: 300,000 (0.3 million- this includes combined of dozens of smaller protestant denominations combined).

The classification of the two Orthodox Churches separately is hard to get. Most government gazettes classify them as one community, since the status of their division/unity has fluctuated over the years.