Currently running Win 7 as a guest OS on Macbook Pro (Mac OS 10.7.5). I have a 750GB disk which is currently allocated 80GB to Host and 670GB (pre-allocated) to VM. (Recognizing now, this was a rookie mistake.) Unfortunately the VM is constantly getting shutdown due to running out of space on the HOST. The host is regularly using 70-73GB of the 80GB. The VM, on the other hand has about 300GB of free space. I've seen lots of posts about how much space to allocate to the Virtual Machine (guest), but haven't found any posts on recommendation for the host system.
Here are my questions:
1) for the life of me I can not understand what is taking up 70GB+ of space on the host. I installed Disk Inventory X and the top 4 folders using disk space (other than the VM) collectively add up to about 20GB. The rest of the folders are <1MB. Where is the rest of my disk space? How can I "recover" it? If I can find the answer to this, I could potentially avoid rebuilding the VM.... 
2) If I were to rebuild my VM (because, apparently, I can not reduce the VM and give back the recovered space to the host and can't find the missing ~50GB in step 1 above), how much should I allocate to the host to ensure I don't run afoul of the Host running out of space? I ask the question this way because I anticipate growing needs for the VM and want to allocate as much as I can to the VM without choking the Host.
Any/all help appreciated.
Thanks!