Mmmm, if you know what you're doing, taking the Indian cities can be a breeeze...
Normally, I take 3 pantodapidoi phalangitai, 2 peltastai and 4 persian archers and go east. I leave the faction leader in Baktra, let my heir lead the army and have the 3rd FM govern Kophen (the settlement just east of Baktra) once I've taken it.
I then train a couple of units of cheap toxitai and get my Basileus
to build forts the other side of the two crossings next to Baktra and have one unit of toxitai garrison each. (You have to make sure the seleukids are neutral, which is easy enough,
as the Parthians usually attack them immediately, so just side with them against the Seleukids. If you are allied, the seleukids will be able to walk past your forts and then siege Baktra, when they first betray you.) (be neutral)
The whole point of building the forts is to buy you time, allowing you to get your army back from India to save Baktra. Using Jirisys's sub-mod, with the realistic movement points, this is perfectly possible, provided you are a confident enough to win these battles.
When conquering India, use your spy to scout their armies. You'll never come across more than half a stack at a time, but fighting in open terrain isn't a good idea. Ideally, move onto a river crossing in their territory and they'll bite. Keep your phalangitai on the crossing, your archers (with flaming arrows) and peltastai (with javelins) on the elephants and you should be fine. Let your general chase down any routers. If you can't manage to manouevre your army to allow a river battle, move your army right up against a mountain range, so that you have a terrain advantage on the battle-map. The ridiculous slopes will tire the enemy while they march towards you, and the extra height will extend your archers' range considerably.
After you win each battle, there should be only one general's unit of elephants left in the regional city, which you should use your peltastai and their javelins to deal with on their own. Garrison the newly conquered settlement with cheap troops and then move onto to the next Indian city, working south. When you have all three, then you will have enough money to start consolidating your position. Use Baktra as your military production settlement and India as your economic hub.
Be careful that the Saka don't invade from the North-East, and that the Seleukids don't attack India from the South-West while you build up, so extra spies in those regions are advised. If you can stop the latter two pulling a sneaky on you, then you have a successful and interesting Mid-game ahead of you. I've only out-lined the part of the strategy for the Early game, as after you've built up, you can go vastly different directions.
