Gst

Principal would supply goods to his depot on payment of CGST+ SGST if supply within the State. If supply interstate then he would charge IGST. he would take credit of either and for further supply again raise an invoice similarly. Importantly the supply of goods is not by the C&FA. Such Principla would need to be registered in all Stateswhere he has a depot.  

The C&F services provided by you in every location and therefore you also would be needed to register in all locations. [ we understand that some services maybe allowed centrlised registration- but only when law comes we will know which ones. ]

As far as your billing from each place of rensdering service is concerned to Principal- for service supplies whether within the State or Outside the State- you could fall under Section 9(9) of the IGSTA which specifies that you need to bill the registered location of the Principal.  As principal wouldbe registered within the State i.e. within your State then CGST + SGST would have to charged.  

Principal can avail the credit. Those with knoweldge of GST to offer their comments.