"My question is can I safely delete all of these in one fail swoop."
Yes. Also download and use CCleaner to regularly clean out these files automatically. click here
Also look at the size system restore is using. It could be taking as much as 4Gb of your hard drive. 1Gb is enough.
As to the extra hard drive, why not put it in your self. It is very easy, 10 minutes and you will get excellent guidance from here. Even a video if you want one.