replies to q's:
1) yes, if there are appropriate scopes setup for each subnet, see next q/a
2) you need multiple scopes on the dhcp server for each subnet:
scope 2 - 10.1.2.0/24, range for ip's, 10.1.2.2 g/w
scope 3 - 10.1.3.0/24, range for ip's, 10.1.3.2 g/w
scope 4 - 10.1.4.0/24, range for ip's, 10.1.4.2 g/w
3) well, you do need a static route in order to get to subnet 10.1.1.0, since that is where the dhcp server is, and the 4200 does not have 10.1.1.0 on it...and if you need to get off any vlans to the wan router for external access, then you'd need a static route in order to get off the 4200 switch...
i also assume you have routing enabled on the MS-ISA server...
4) in order to dhcp relay, you are required to have an ip addr on vlan5, but since you don't want routing on that vlan, then yes you will need a separate dhcp server for that vlan...(or separate NIC for vlan5 in the dhcp server and routing -not- enabled on that server)
5) they look basically ok...
hth...jeff