Stop using WDS as the solution. Use MDT. Use a thin image. Enable multicast buy make sure your network has the necessary settings configured otherwise multicast traffic will flood your network. Don't perform multicast over wan links either.
You can uses sccm and SCUP to push out the latest flash using wsus. This gets around the issue. I guess it comes down to adobe being paid when home users don't untick the adware that gets installed with adobe flash.
First login to a PC takes 4 mins. 1st login for a user about 2 mins. Then about 1 min about which. It shorter if the PC gets logged off. This is probably due the prefetch.