Hi @Tom, nice to hear from you.
The file I downloaded is reported as 1.45Gb by Windows (10) and is called UnitySetup-4.6.9, might be worth double-checking the file you have though, as that’s quite a big difference in file size isn’t it.
With regards to glibsharpglue-2.dll, I don’t personally ever remember downloading that, I was using 4.6.3 at the time, so I would imagine it has been fixed. As it appears that it was only an issue with MonoDevelop launching correctly what I would suggest is running the installer for Unity (after checking you have the right file etc) and then literally giving it ago.
You will be accessing the Scripts fairly early on in the course, so you will have a chance to test whether MonoDevelop launches correctly or not. If it doesn’t, then maybe give that additional file ago.
Alternatively, you could always consider grabbing a copy of Visual Studio, you may find in the long term this is a more useful/powerful IDE, but maybe just get into the course and check a few things first.
Give me a shout here if you have any issues and if I can help I will, there is of course the specific Q&A against each lecture on Udemy also, for specific course related questions.
Hope this helps.