1. Typically, how long does it take to complete all the formalities of getting a Green Card in the USA after one has got his labor certification approval?

2. I am an Indian, if I marry a girl who is staying in India after I had got my green card, how long does she need to wait before she can move in to the US?

3. If I go back to India permanently after I getting the US green card yet want to keep the green card alive, how frequently do I need to visit USA and for how long should I stay in each visits?

Answers are appreciated.
Thanks

If you get a GC and then marry a girl in India, she will be stuck there for no less than 4 years. Sometime even more.

Once you have a GC you need to visit US every year or sometime every 6 months. However you can take a re-entry permit and not visit for 2 years.