"1) How to configure the 12 disks in the MSA? One big raid set, or separate raid sets for each server?"
Bear in mind that the maximum LUN size ESX(i) will recognize is 2 TB - 512K. With the configuration you described I tend to keep my LUNs a bit smaller because of the way I/O is queued. My recommendation in your case would be either 3 or 4 LUNs of either 4 or 3 drives each.
If you really don't care about redundancy you could use RAID0 - that will stripe the data across the drives, but in the event of a drive failure you will lose all of the data on the LUN. Personally, my performance needs are moderate so I create RAID5 LUNs. By doing so you get about the same read performance as RAID0, but suffer a bit on write performance.
If maximum performance is desired, I would create two RAID10 LUNs, six drives mirrored in each.
See
http://en.wikipedia.org/wiki/Standard_RAID_levels for a discussion of RAID levels.
The local drives in the servers I would conigure as a mirrored set before the OS install.
"2) I addition, do i create one big datastre on the vmware server, or seperate datastore for each server?"
Actually I would do something in between and create a datastore for each LUN. If you have need for a larger datastore you can add extents.
"3) Memory configuration, any thougts?"
Get as much as you can afford. VMware is RAM hungry.
"4) NIC : i have only four nics on each server. Should i orde additional nics to assure every server has its own unique nic, or is nic sharing OK?"
Four NICs should be plenty to get you started. would configure them into two redundant pairs, one for the service console and vmotion (and possibly light VM traffic), the other pair to accomodate the bulk of your VM traffic. If you need more NICs you can easily add them later.
Good Luck
