I'm not a professional but here are my few cents regarding your doubts.
1. The higher the gear you coast in, the lesser will be the fuel consumption.
Whether the car is coasting in a flat surface or on a downhill, the fuel consumption remains the same as long as you are in the same gear.
2. No, it is not a good habit at all. It puts unnecessary pressure on the brake system. I recommend pulling the handbrake if there is a long gap between the signal.
3. It does effect the car's Wheel Alignment. Its recommended to keep the wheels straight when parking for long time.
4. Though manufacturers say, new generation cars doesn't have any run-in period. There are people who still follow that. I would any day follow it, just like an extra precaution.
5. Sometimes, quick upshifting can give you more FE. But its better for the engine if you upshift only at the recommended rpms.
6. If you are in a good momentum, then I guess its fine. I have been doing it for quite some time. But make sure the car is not at halt. I believe there will be a very slight FE increase. Please don't kill your clutch in the process of trying to achieve more FE.
7. I'm not sure about this one. Just change it if you find the engine oil to be too dark. 10k is fine I guess. Many manufacturers change their oil at 15k kms.
8. Everyday, when I start the car, the car is left for about 30 secs approx. to warm up. If the car has been left untouched, then more.
I never heard about idling being dangerous to the engine
, it causes damage only when you rev the engine before it reaches its optimum temperature.