Status Change from L1B to F1 - Questions - Please help

[RSu11]

Hi , 

I am currently in US on L1 B status & as per company's policy I have to leave US by June end. But i got L1B visa & I-94 until dec 2019.
I am looking for schools to join for master's and currently i have the i20 from university .

I have following question regarging COS process from L1 to F1. Can some one please suggest on 

1) Can i attend the classes while my COS application is Processing?
2) If i apply for COS based on the current i20 now ,can i switch the university when i find an better option before joining ? Do i need to submit another application or any doc's?
3) If my COS applcation got approved before classes start, can i stay in US till semester starts? and Can i work till classes start?
4) If my employer terminted my L1B by end of june and class starts in august, can i stay in USA with my COS application in processing status?
5) Best time to resign my job? After COS application got accepted by USCIS? Or Once COS approved? waiting until employer terminted L1B?

Thanks
Teja