Would it be a good idea to add a little bit of GH booster to new Controsoil?
Depends on the water you are putting in. Since this is a buffering substrate, you really should be using RO at which point you will need GH booster.
If keeping shrimp, you'll be using remineralizer, and if you are doing it right, you'll be letting the tank mature before adding shrimp. By the time that happens, the soil will be "charged" and will stop pulling noticeable amounts nutrients from the water column.