Since you already have vSphere Essentials Plus license.
if you upgrade your hosts from 1 socket to 2 sockets also, upto 3 hosts license is valid. (your environment has 3 hosts currently as I can see from the description)
now, if you want to upgrade Essentials Plus to other vSphere Editions, your options are go for vSphere Standard, Enterprise or Enterprise Plus edition. Take a look at following URL to see comparison between features being offered.
Thank you for you reply,
Understood for essentials plus license.
Then, if we want to upgrade and get more functionality, we must purchase: 1 vsphere license per host (standard, enterprise or enterprise plus) and 1 vcenter server standard license, isn't it?
vSphere Std/Ent/Ent. Plus license works based on CPU sockets.
let's say you have 3 hosts, each with 2 sockets (unlimited cores per socket) then you got to buy 6 Socket license.
and to manage those hosts, you need 1 instance vCenter standard license.
hope this helps.
Thank you, this is clear