some answers below but I would like also like to know the answer for (c) around the subnet scanning
a) I believe yes the admin guide says it can be installed as a standalone product
c) I am interested to find out more about this well
d) I dont believe so, i've disabled ICMP scanning and it gets next to no information from the router other than the reserved IP Address for the interfaces (I've also got no DHCP server enabled)
e) SNMP discovers the subnets using the routing table from the routers instead of manually having to import.
Thank you for your answer. It would be appreciable if any one could help us in this.