A couple of things: Running Vista with 512MB of RAM? I'm not sure I would recommend that especially when you start loading up Office applications inside there.
Second: Are you going to use persistent or non-persistent pools? If you use persistent are you going to allocate a user disk?
There are some best practices on what to do with linked clones to keep your disk usage down. I would have to hunt them down. Things like pagefiles, hibernation files (on by default in Vista), temp files, etc. will all bloat your delta disks to a point of reducing your savings on the linked clones. Because of page sharing your memory utilization per workstation will be less than the actual RAM allocated. If you keep all the desktops uniform the memory page sharing will reduce any duplicated memory pages so that multiple machines only use that single page. You will in essence be able to overcommit the physical RAM in the machine. So in your case with 16GB x 4 = 64GB of RAM, allocating the 70GB of RAM is not a problem. However, i would consider raising the RAM allocation per workstation to 1GB. Of course if the performance is there for you, great.
Is there any reason you are looking at running Vista in the VM environment? I find that XP is far more capable and certainly less resource intensive. We run XP with 10GB disks and have had no problems so far. Of course I have not yet scaled as high as 140 (still in wide testing).
One final note (sorry so scatterbrained, it's early), you may run into some performance issues with 140 machines on a single LUN. It all depends on your spindles, etc. Once again I would seek out the best practices information and see what is recommended there. A lot of this is testing to know if the performance takes a hit with that many VMs on a LUN. Every situation is different.
