1. For both we can use or not the active directory, if we integrate we can discover..
2. If you are using same DB means install 5 different SEPMs and SQL as one( Should be high power)
3. Its based on Domain ID install the SEPM as first site so it will not disturb the others
4. Yes u can, but you need to add other site as replica
5. No it will not change AD scheme..for desktop recovery it is very essential to have AD
6. only one agent is enough
7. Always make sure all the policies easily identicable and tracable in future.,