L1B extension under new blanket

[Shekar18]

I came here in 2016 November (so completed only 2yrs) with L1B blanket Visa and it is expiring in march 2019. My company started processing the L1B extension under a new blanket different from original one as my company was spun off from its parent in 2017. So I would like to understand how the Visa officer/USCIS treats my application -  as a new L1B or an extension?

2. When I am filling my DS-160 (or I-129s) what should I put  in start date - date after my current visa expiry 3/27? or any date prior? - does it affect my current visa?

3. If everything goes trough - my visa can be approved 2 years or 3 years?

your help is highly appreciated.