I am employed with a company on L1B visa and visa is valid till March, 2014. I want to get it converted to H1B in April, 2013, if I get a sponsor.

Considering that I get a H1B visa sponsor and I get L1B converted to H1B, I have following queries:

1) When the H1B would be effective? (means from the day my petition is approved or from 1-Oct-2013)

2) Do I need to get VISA stamped? (I understand I need to get Visa stamped only if I am planning to travel outside USA. Correct me if I am wrong.)

3) If I have to get Visa stamped, do I need to go back to my home country or can I get it done through some other country like Canada or Mexico?

Please share authentic information with references...
Thanks for your help advance!!