VMWare ESX server does not recognize RAID 10 datastore

Given your application profile (i.e. doesn't sound like it's going to be doing too much writing) I'd say you'll be just fine with R6. Oh and worry more about how many VMs you store in a single datastore/LUN (keep to less than 4 for decent performance) than how many VMs are managed by the array.

As the others have mentioned the ESX Service Console user environment is not really optimized for performance so apps that are not specifically designed to interface with ESX tend to perform very poorly. Veeam FastSCP generally outperforms anything else that I've tried for copying data directly to\from\between ESX and ESXi hosts and it's worth trying that if you are dealing with multiple ESX(i) systems but if you are moving stuff around (or copying) within the one ESX host then the VI Client or the native console interface\remote CLI tools are what you should be using.

vmkfstools -i (import) is the recommended way to do this from the command line, you can find some details on the syntax here but use man vmkfstools from the ESX console for accurate syntax.