Excise registration as first stage dealer

Dear Sir,

A chemical company based at Mumbai (manufacturing plant)  having branch office at Vijayawada, till date supplying goods to its branch by taking VAT in AP. The company has appointed one C&F agent to lookafter all branch stock movements. 

The comapny is already having VAT registration and also completed GST registration procedure under VAT.

Because of GST, the company wants to register itself as First Stage Dealer under central excise at Vijayawada to get tax credit on opening stock.

What is the procedure to register as First Stage Dealer in the above situation?

What are the invoicing formalities to comply?

How to pass tax credit to second stage dealer (till the date of GST come in to force)?

Please give your valuable suggestions.

Thanks in advance..

Swakar