The HISM is very simple:
// creating HISM once
hismc = NewObject<UInstancedStaticMeshComponent>(this);
hismc->RegisterComponent();
hismc->SetStaticMesh(YourMeshReference);
hismc->SetMaterial(0, YourMeshReference->GetMaterial(0));
AddInstanceComponent(hismc);
// and then instaniation
FTransform t = FTransform();
t.SetLocation(NewLoc);
hismc->AddInstance(t);
Also I recomend to use per instance custom data to modify tile material instead of material instances, it will reduce draw calls without serious restrictions. For this technique you need to setup your hism material data floats by hismc->NumCustomDataFloats = <num of needed floats>
https://www.ue4community.wiki/using-…-mesh-bpiygo0s
About grid data I dont know your game mechanics, it depends on what you want.