1) India collapses. To get my 10 cities, I'm forced to settle 1 city in a contested area, and take 2 from the Tamil.
You aren't forced to settle in any contested areas. I just loaded up a save from my Monarch UHV run, and I have 10 cities covering every tile on the subcontinent. The only city I have in a contested area is Tanjapuri (the southernmost Tamil city). So in addition to the 2 starting cities and the 2 Tamil cities, I founded six in historical areas. They are, in order:
Chittagong, founded 724 BC to the East of capital, 1S of Rice. The gold here will help your economy, and it's so close to your capital that city maintenance is very low.
Ashaval, founded 369 BC 1W of Horses: This city is absolutely critical as your source of Horse and Marble.. Focus on culture so you don't lose the Marble if Persia founds Pura.
Nagpur, founded 324 BC 1S of Iron: This will be the key to your defense against barbs
Panaji, founded 229 BC on the West coast 2W of Spices and 1S of Gems. This is the only way to get the Fish next to it - don't worry, it won't flip on Tamil Spawn
Kolkata, founded 69 BC 3S and 1E of capital. Founded it later because we already have the resources it provides, even though it's so close to capital.
Srinagar, founded 64 BC on the plains hill north of the Sheep in the northwest. Most tiles around here are contested, but this one is actually historical.
2) If I don't HARD FOCUS on UHV#1 starting from turn 1, I lose. In fact, by doing this, I barely get it anyways. I think around 300 BC or so is when I get my second shrine.
If you're focusing so hard on UHV1 that it hurts your early economy/expansion, don't focus so hard. You have until 100 BC, so use the time you have. My second shrine came online at 174 BC.
3) If hinduism doesn't spread to the the bigger of the 2 cities that you get on the start, it's basically a loss, btw.
Why? The two GPs to build your shrines should come from the capital, because it has a ton of food and the first shrine gives you 3 more Priest slots. If Hinduism takes awhile to spread to Indrarastha, you can actually benefit from it by building a Vedic Temple there. Once Hinduism does arrive, it'll be converted to a (much more expensive) Hindu Mandir for free, saving you a bundle of hammers. With Pataliputra providing both GPs, Indraprastha's decent production is freed up for expansion and economic development.
What did the domestic adviser say about your stability leading up to your collapse, and what are your civics? If I know which category was dragging it down, I could offer some suggestions to help. In general though, try to have a Jail in every city (Citizenship civic helps for building them) and lots of excess happiness, which you should have just from your many plantation resources.