So I should build Pitikapuram in the game with Takshashila, I take it?
Not sure what the name of the city is, but it is on the cleared grassland tile on the coast at the mouth of the Ganges. In the 600AD start, this city is called Patna but is not on the coast - which is much poorer as a location.
I may do that, but building more cities hurts my stability doesn't it? In the Takshashila game I'm already at unstable. Or does filling out the empire boost it?
There is a (very minor) stability penalty for each city that you control. This penalty is significantly increased if the location is outside your civ's "core area" (historical limits of expansion) and significantly increased again if the city is in another civ's core area. There's more to it than just this, but that is how I basically understand it to work.
But there is a bonus to your expansion stability component for adding territory to your empire. I believe this outweighs the penalty (certainly for cities within your core area) for each city though.
When you say that you are unstable, what components of stability does the F2 screen indicate are less than 3 stars?
One large stability problem for India I forgot to mention earlier is that if you have adopted a state religion, each other religion in any of your cities adds to the instability. The solution for India: Free Religion. Get it via the Shwedagon Paya if you can't research FR faster than you are becoming unstable.
I don't have any vassals, and my military in the Takshashila game is utterly pathetic. I could spend 20-30 turns after I get Divine Right going for all the usual suspects (Swordsmen etc) and I can even get up to War Elephants at one point. The problem is I'd probably be better off hitting Persia and trying to get them to capitulate for the purpose of Viceroyalty, but again, if I'm already unstable I'm not sure how much expansion I can even do.
India only needs two types of units: cheap defenders and elephants. You neither need nor should expand into Persia in my opinion. Try to take up the space between yourself and the Khmer instead and the southern bits of India. Then look to Java (sorry I called the island Jakarta before by mistake) or Singapore or even Australia after that. Elephants are all that are required to control and/or remove the independents/Khmers from these areas.
How the hell do you get to Biology far enough before 1200 AD to matter?
You don't, sorry. I played on after my Indian UHV to eventually getting a Diplomatic victory with the UN after finishing the Tech tree, so I made a priority of Biology to clear away all that jungle and the negative effects it gives (mainly health issues).
In case it isn't obvious, I only have a sort of tangential idea of how stability works, because the stupid thing doesn't tell me ANYTHING. I really wish there was something like the diplomacy thing, "-2 Your empire is beyond historical borders" or whatever.
Stability could be explained in more detail, true, but part of the experience of RFC I found was establishing what did and didn't help me to stabilize.