L2 EAD to H1B change of Status

Currently I am working in USA on L2 EAD valid until March 2019 and previously worked on F1 OPT till Aug 15, 2017. My H1b got approved this year to start from Oct 1, 2017 with a 1 year validity. Few clarifications required on

  1. Am i eligible for Cap Exempt ?
  2. Do i have to file COS (change of status) from L2 Visa to H1B (or) status is automatically changed from L2 to H1 from Oct 1, 2017?
  3. If my status to H1B is not Automatically changed, can I continue working on L2 EAD for few months and change to H1 later point of time before expiry? 4) How many days before my employer need to start H1B extension before expiration Sep’ 2018?

Thanks in advance if someone can help with clarifications.