See answers below.
1. Do i need to continue with the company while my 485 is processing (CP)
2. What kind of documents i need from the company to process 485.
Tax and financials including personal docs. The company must be able to prove they can pay your salarly as given in PERM. Remember, GC is for future employment.
3. How long do i need to continue with my current company once i receive my temporary Visa/GC.
There is no legal requirement but if you intend to get Citizenship, it is adviced that you stay for close a year - unless absolutely not possible.
4. Is it mandatory to travel thru the company which processed my GC or can i switch the job and travel for diffrent company job offer.
There is no restriction on travel to the US after you get your GC or even advance parole.
5. How much does it cost for processing 485 alone including the lawyer costs.
Last stage: $1500
Please remember that once you get PERM approved and I-485 approved. You can be asked to pay for the last step - which is: Change of Status. I do not think there is any law stopping a company from asking you to pay that part.
Please consult attorney.