For question 1, whichever host interfaces with the LUN first is your os-type. If it's a VMware DS this Windows host lives within or if it's a Raw Device Mapping, the igroup os-type would be VMware. If this is a physical Windows host you're presenting directly to then os-type Windows. I may be misunderstanding the question though.
#2 -- If it's a physical box I would definitely put the MPIO DSM on. If it's VMware guest, make sure the Host Utilities are installed on the VMware host. (I think the MPIO DSM for ESX is in the Host Utilities package. Double check that part, as I'm not 100% confident that is the case.)
#3 -- On the Windows side you can set the LUN read-only with diskpart. Select your volume then do "attributes volume set readonly." If that doesn't work as intended for you "attributes volume clear readonly" to revert.