Recommended SSD size? Can pfSense manage traffic speed out of the box?

So I already bought the motherboard/CPU, an HP NIC and 4GB of RAM. I already have a spare case from an old Dell and about 3 power supplies.

Anyway, I have a spare SSD of 120GB and a HDD of 80GB. However, I'm guessing that pfSense doesn't require a lot, right? I'd rather buy a smaller SSD from eBay. But how small? Is 16GB sufficient?

I just need the firewall, Snort or Suricata (which is more user friendly?) and maybe something else if you guys happen to have something in mind. I would REALLY want to block certain sites and manage traffic speeds as well (against Netflix for others at home). Or will I need to install something else?

This box I'm building is just for home use under crappy 18/0.9 speeds but with 20 wireless devices and 5 physically connected computers/games at a time. I'm new to this and have never built a pfSense machine. Thanks for your time!