RAM is mostly used by map - other server features, website or database barely uses any. Load it once and check how much is taking in your system to measure how much you'll need.
TFS is not multithreaded and it doesn't really take much CPU to run aslong as scripts are decent optimized. Any desktop/server CPU from this decade (or even century/millenium xD) will run just fine.
As of network... it depends. If you are going to have many players in one place or scattered around the map - it may vary a lot. You should be fine to host a 100 player server in a 10-20mb connection. As always - fiber/cable and wired recommended.