Hello again, John,
I am sorry to hear that you are one of the very few people who continue to have problems. I know you have tried many things to resolve this and been unsuccessful, and I wish I could give you a "silver bullet" answer. But I don't know what to suggest.
The types of errors you have been getting and continue to receive continue to be consistent with some other program interfering with TMG. The error "Someone else is using the selected project and it is not possible to restore it." is a perfect example. I know you said that you did a "normal install, limiting programs", but I am still suspicious there is some other program causing all this. One other user did not know about DropBox and was not intentionally running it, but her system did automatically install it, and she was able to discover it was running. When she was finally able to stop it, all her problems similar to yours went away. So it still may be some program on your system which you are not aware is running.
By the way, just to try something, whenever I Restore a project, I first Exit TMG so it closes completely. Then I open it and do the Restore. In the guise of "trying anything once" this might help, although it "shouldn't" be necessary.
Continuing trying to help,