"VSAN THREE SITES OR FOUR SITES?"
Do you mean nodes or sites? Minimal set-up for vSAN is 3 nodes (or 2 data-nodes + 1 Witness), if one is talking 'sites' then this usually indicates stretched clusters which consist of 1-15 data-nodes on 2 'sites' + Witness so saying 4 sites makes little sense.
"TWO DATA CENTER LINK MODE (NESTED)
ONE FOR NSX (I DON’T KNOW IF IT BETTER IDEA TO INCLUDE IN BOTH DC?"
Please read the requirements documentation for these products - they require a significant amount of real RAM to function:
vCenter = ~10GB minimum per vCSA (6.x)
NSX = ~22GB+ on version 6.2
vSAN = ~10GB per node with your current cache-tier size configuration:
Basically, you likely don't have the gear to run all of the above so pick and choose - do you want/need a vSAN cluster or do you want/need to test NSX?
You likely can't do both here.
If you want to test these products with zero hardware investment, there is always HOL:
There is an abundance of information already available:
Please also consider checking if your caps-lock key is broken (most would just assume you are SHOUTING )
"i can add more Physical Ram if needed."
Yes, if you want to run NSX, multiple vCenters and vSAN hosts with the disk configuration and assigned memory you outlined you will likely have to go 128GB (or assign less memory to the hosts and go 96GB - though this may be tight).
"please advise and add you experience."
Sorry but your diagrams don't make much logical sense:
For starters, what do you mean by 'Data Centers' here? If you mean vSphere logical Datacenters (as you would have in vCenter inventory) then this would imply that you intend to create multiple vSAN clusters in different Datacenter/vCenters?
All members of a vSAN cluster have to be managed by the same vCenter and must reside under the same Datacenter Object.
You have "Node1 (cluster1), Node2 (cluster2)" - vSAN requires minimum of 3 nodes per cluster (or 2 data-nodes + 1 Witness).
Then you have "node3, node4" in another Datacenter with no indication of what these are clustered with (each other? cluster1/cluster2?).
If you do not yet have experience with setting-up/administrating vSAN environments I would strongly advise spending some time building (and dismantling!) some clusters using HOL: