Yes you CAN, but you shouldn't.
Opening a web server (and ESPECIALLY an FTP server) opens you up to a plethora of vulnerabilities that you wouldn't have had with a desktop and (hardware!) firewall. You need to be aware of what you're getting into.
Commercial sites separate externally visible web and FTP and mail servers into separate networks from their desktops. At work, we have several different networks (public, visiting scientist, operational, data pipelining, development), each separated from each other. For a reason. We don't have the nasa.gov domain, so we aren't the obvious target some other folks here are, but having a virus go through the building would be a disaster.
It doesn't take much power to make a web server. You'll be limited by your network, not the computer itself. So, pick up the headless motherboard and disk your neighbor is throwing away and use that.
And depending on Microsoft for security is a fool's errand. Do NOT depend on that POS "software" firewall, when you can buy one in hardware (that doesn't have access to your OS!) for $20.