I went to download this, and ran it through a virus checker as I do with every file, and it reported that it was carrying multiple viruses. Is there something in here that virus checkers report that isn't actually a virus, or did I click on the wrong download button or something? (Unlikely, as it was labelled as RS2014customtoolkit or something along the lines of that.

False positives are common with antivirus programs, especially niche ones that aren't common worldwide. If you want many second opinions you can scan a file or URL (for the file download) here:

https://www.virustotal.com

@@scrummer Nothing sinister is lurking in the toolkit if you downloaded it from the official site here.  Typically AV's throw false positives with auto updaters because they act like a trojan would.  You can whitelist the exe's contained in the zip archive to avoid false positives in the future.