Queries related to AD migration

Hi Team,

  We are working for a AD Consolidation project. I have few queries related to QMM AD set up

1) Is it recommended to have ADLDS in separate server or we can keep the same with QMM?

2) Suppose existing environment has 3 forest and will be consolidated to one. So for each domain pair do we require separate server and install QMM in each of them?

3) When we should use Rumming?