EB-1C International Managers, Executives

My PD - July 2014 EB2. I have a pending 485 and got EAD and AP.
I’m a manager in my current company and manage teams in India and the US.
I would like to know how to upgrade to EB1 as International Manager.
Is it required that I work outside the US for one year?
If I visit India and work for 3-4 months, can the accumulated time over 2-3 years be used for upgrading to EB1?
I would also like to know if we can renew EAD from India and keep the current 485 processes on track.
 

Who pays for the I-140 filing fee? Employer or Employee? Do federal regulations mandate payment by the employer? Who pays the attorney fees for the I-140 form per federal regulations? Is it mandatory to be paid by the employer? Who pays for the I-1485 filing fee per federal regulations? Employer or Employee? Any federal mandate I need to know? Who pays for I-485 attorney fees per federal regulations? Is anything mandated in federal regulations?
 

How does EB-1C portability work?

I also have a question about the EB1C portability of the priority date. Say, If I have I-140 approved under EB1C and have a particular priority date. For some reason, if I need to or want to change employers and I do not qualify for EB1C with other employers. My new employer can file I-140 under EB-2, or I can file EB-2 NIW myself. I have both options. The question is whether I can use the priority date of the earlier approved I-140 petition under EB1C to the new employer's EB-2 petition and file AOS.