1. I guess you're asking about a COS-Change of Status? The max period of stay on an L-1B is 5 years. You will have to remain outside the US for 1 year before you become eligible for a brand new period, i.e. 6 years on an H-1B. But you can get 1 year on H-1B if you only have had 5 years on the L-1B. But you can't claim the other 5 years until you stay outside the US for 1 year.
2. You can but only get the 1 year maximum plus additional time until October, so if you leave in March and enter on September 30, 2013, you approximately 5 1/2 months of being outside the US, but USCIS will probably give you 1 year validity on the H-1B and then later you can recapture this, but max would be 17 1/2 months on your H-1B.
You can switch to other non-immigrant visas, like the H-4, O, E, etc but the only way to get a new time is to physically be outside the US. So, if you qualify for an O visa, max stay is 5 years, you can remain here, but you can't later after that 5 years, switch back to an H-1B since you are max out. You got to physically be outside the US for 1 year to get a fresh start for an H or L.
3. Not negatively but it will eat into (take away) from your 1 year max time outside the US.
Mr. Calehr gave an excellent analysis.
PROFESSOR OF IMMIGRATION LAW for over 10 years -- This blog posting is offered for informational purposes only. It does not constitute an attorney-client relationship. Also, keep in mind that this is an INTERNET BLOG. You should not rely on anything you read here to make decisions which impact on your life. Meet with an attorney, via Skype, or in person, to obtain competent personal and professional guidance.
1. What is LOS?
Your H-1B will be limited to one year.
Your employer needs to retain an experienced immigration lawyer, whether myself or one of my colleagues, to review all the facts, advise them, and handle the case.
J Charles Ferrari Eng & Nishimura 213.622.2255 The statement above is general in nature and does not constitute legal advice, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship. Answers on Avvo can only be general ones, as specific answers would require knowledge of all the facts. As such, they may or may not apply to the question.