Hi ,
You have check server h/w compatibility with vsphere version , installing Esxi no need of 2 tb . you can create separate Raid on device if it supports .
use 50 Gb for esxi and other create another raid with local data store . or use single Data store .
shutdown vms and remove from inventory
disconnected NAS
New server install esxi - > connect NAS -> Register one VM ->take snapshot -> upgrade vm h/w -> power on and test .
If working fine proceed same others .