What are the minimum hardware requirements for a DarkRP 100+ players GMOD Server?

Youd need most likely a dedicated core version of one of the top cores in this list.
http://www.cpubenchmark.net/singleThread.html

Gmod is HIGHLY CPU intensive. RAM you should be able to get away with 4GB and your bandwidth seems fine.
Oh and dont try to run intensive addons, youll just roast your CPU even more.