After reading your post I can't help but think, for a moment anyway, under the circumstances why on earth don't you just have a PC to run Windows. (Although Windows does run better on a Mac then a PC! 
) I know you said "(Recognizing now, this was a rookie mistake.) " nonetheless to me pre-allocating ~90% of the Host's HDD/SSD, regardless of its size, for a Virtual Machine (or just about anything else) is absurd and would never do it under any circumstance.
Anyway, I think that regardless of what's taking up space other then the Virtual Machine is irrelevant and the Virtual Machine's virtual hard disk should be resized downwards however this cannot be done once a virtual hard disk is partitioned/formatted however there are options. Because you do not have adequate free disk space on the Host to perform any maintenance on the Virtual Machine you'll need to use external storage like a Firewire/Thunderbolt/USB HDD to help get out of this mess.
Two choices come to mind, either use disk imaging software like Symantec Norton Ghost to do disk to disk imaging to a smaller right-sized disk and then swap out the virtual had disks or install VMware vCenter Converter into the Virtual Machine and then create a new VM from within the VM to the external storage while customizing the size of the virtual hard disk to a smaller right-sized disk as you walk through the Wizard. Personally I'd choose to use disk imaging software.