Additional Place Of business at other State

dear experts.

FACT of the case is.
ABC pvt ltd having head office at Maharashtra (Registered) and
1 branch office at kerala (Registered)
1 branch office at Gujarat (Registered)
all three places are registered under GST in their respective State.

all purchases are done at Maharashtra head office and then supplied to customers and also to branch offices via tax invoice.

Branch transfer is done at cost + profit and treated as normal sale at head office.

Query.
1 - Can ABC pvt Ltd do centralise billing from Maharashtra for all supply made through branch offices also??
and do the stock transfer at cost price only.

2 - ABC pvt ltd wants to take on rent a warehouse at Tamil Nadu but don't want to register that under GST. as they want to do billing from Maharashtra head office.

kindly give ur expert opinion.

thanks