For how long will the H1B visa be valid for entry to US

Consider the case my H1B petition is picked up in the lottery and it goes through the processing phase. Due to various personal reasons it may not be possible to go to US immediately…in that case

  1. How early should i go to US?

  2. If i don’t go for Visa stamping, how long can i stay away from stamping?

  3. If stamping is done and i go to US and work for couple of months and return back to settle down the issues. From this point of time how long can i stay back in India?

  4. Will there be a chance for my petition/visa getting into invalid state?

Please let me know these clarifications