Interiors design contractor comes under works contract?

I have many questions regarding the Interior design contract business,

1. Does it comes under works contract? If yes, Is ITC not allowed?

2. As it is considered as a service, is the SAC 998391 correct for contractor?

3. If the contractor have gave service to any government authority will it be taxed at 12% or normal 18%.

4. Are there any unusual provision under GST for this kind of business.