Hi,
re 1) yes, with the VM running you cannot make a reliable backup using that method. Suspending your VM should work OK.
Pausing however is unreliable as whatever is in memory is not written out to disk. Note that Pausing is not the same as Suspending. Also note that it is possible to make backups of running VMs as that's exactly what I do with my backup product, but it uses VMware snapshot technology to do so.
re 2) it is entirely up to the guest OS if it writes out to the virtual disk. Note that you can have multiple levels of caching here (host OS and guest OS). With suspends you should be fine (once the suspend is finished writing!)
re 3) yes you can always change between split files and monolithic going back and forward.
--
Wil
