L1 to h1b transfer doubts

USA H1B Visa
1

Posting for friend,kindly need experience :

Current status :
a)L1 and completed 4 years in US at present and filled 2nd extension(march 2021) still in
processing.

b)H1b 2021 lottery picked up and attorney yet need to fill documents

few queires:

  1. Can he work still in L1 even if h1b approved

  2. is it mandatory from October need to work on h1b

  3. I know COS applying, is there specific we need to let tell attorney specific while submitting documents.

  4. if h1b approved before L1 extension approval, what will happend to L1

  5. if L1 extension gets denied, can still wait to see upto H1b approval status in the US.

  6. If h1b approved, is it will be fresh can be utilized for next 6 years or
    (already 4 years L1 completed pending years only h1b need to be used)