What will be GST SAC code and rate on Swimming Pool for commercial training purpose ...?

One of my frnd wants to start Swimming Pool for Training and entertainment purpose he is already having GSTIN.

but this GSTIN was of his other business Now the Questions are --

1) whether he has to ament GSTIN and add the POOL business ?

2) what will be the SAC code for this?

3)What is GST rate on fees for coaching Swimming ?

4)What other registration has to be adopt for this Pool Business ?

Please suggest...

thanks in advance....