Virtual machines cannot access your SAN directly and access the SAN storage via the host servers SAN connection. So you can have as many virtual machines as you want accessing your SAN storage through your ESX host. You can mix virtual machines on local and SAN storage on a ESX host. So in your case you would only be using 2 SAN ports on your switch, one for each ESX host. If you wanted to multi-path for redundancy then you could add a second FC card in each host. With local storage only the specific host server can access the virtual machine and you cannot use features that required SAN storage like vMotion, DRS and HA. You can also move VM’s back and forth from local storage to shared storage by performing a cold migration or using the new Storage VMotion feature. With ESX you can setup many datastores to different types of storage devices like NFS, FC, Local Storage and iSCSI.
Is VirtualCenter worth the extra cost? It depends if you want to use features that require it like HA, DRS and VMotion. Even with 2 hosts some of the extra features (templates, AD integration, Update Manager, cloning, historical performance monitoring, capacity planner, integrated P2V) are worth it. VMware has some SMB Foundation Pack bundles available for 2 ESX hosts with VirtualCenter bundled at a reduced cost that you might check out