H1 Visa transfer and visa stamping

[Hariit]

Hi ,

I am having h1B visa stamping valid till Sept'15 and this is my 3rd year on this H1 and i have a dependent on h4
Now i am planning to change my employer. My questions are

1.If i get my H1B visa transferred will my H1B get extended for the next 3 years
or
After my transfer to the new employer is done do i need to apply for an extension again?

2. H1B visa stamping:
a. When should i Get my visa stamped? After my transfer or extension is completed or before the expiry of stamping?
b. Can i stay in US even if my H1 stamping is expired?
c. If my H1 Stamping is expired and i traveled to India what should i do when coming back to US?

3. What should I do for the dependent if my H1 gets extended?

Thanks in Advance!!
Haritha