Welcome to Communities.
"- 1 site with 2 rooms"
What's the distance between the "2 rooms" that you are considering a Stretched-cluster as opposed to a regular cluster? If you are running a Stretched-cluster you will also need a Witness running somewhere else.
"Do we need only 1 vcentre for all the clsuter ?"
All vSAN cluster members must reside in the same vSphere cluster so yes they need to be in the same vCenter inventory and you only require 1 vCenter - that being said, it is of course supported to have multiple vCenters e.g. in Linked Mode etc.
"Dowe need 1 NSX-T Manager instance for all cluster ?"
Yes you only need 1.