track 1 interface Serial0/3/0 line-protocol track just can adjust the weight . in interface config mode ,u can glbp 1 weighting track 1 decrement xxx

The controller should take over all the jobs of the failed controller :ip、mac etc.the controller must be in the same vlan. do not worry anything .

the two MDS switchs will be a fabric when they are connected,one VSAN only have a active zoneset.now 2 MDS switchs have two zoneset ,one zoneset will be useless.

400MB/S is just a average value in 5min .

u can config ip dhcp excluded-address for every swtich . for example ip dhcp excluded-address 192.168.0.1 192.168.0.127 ;the other is ip dhcp excluded-address 192.168.0.128 192.168.0.254. the ip address can not conflict .u must be sure any one switch...