Clarification of GST on Labour Charges

Dears,

We are registered in Gujarat state. We got a composite works contract order in Karnataka state from a Private company. We do not have registration in Karnataka state. We intend to supply materials and want to hire a labour contractor to do erection works at site who is registered in Karnataka state. 

Question -

1. Which GST will labour contractor charge IGST or CGST+SGST?

2. Will we get GST ITC credit of labour charges, if CGST+SGST be charged and same if it charges IGST (we are not registered in Karnataka state)?

3. if labour contractor is not registered then, are we required to GST under RCM?