Allan,
No need to create a second vCenter, if you have already a vCenter you can use it. With HA in case of a host failure, the vCenter will be restarted on the other host.
For me , choice the first one . Because if you choice the second recommandation you will loose the investissement of your local storage (4TB).
Then , please call VMware Sales, they will be better than me to discuss costs 
. I am just an engineer 
Contact Sales
Regards,
Julien.