Since you are looking at implementing a VDI you will want to take a look at VMware View - VMware Horizon View (formerly VMware View) (VDI), Virtual Desktop Manager | United States - they do have a bundled package that includes all the components that you will need -
If you are looking at virtualizing servers you will need a copy of vCenter Standard because you are looking to manage 4 ESXi hosts - the level you want to purchase (Standard, Enterprise or Enterprise Plus) will depend on the features you desire -
I have also moved this to more appropriate forum -