My goal is to create something that is absolutely secure and safe from any kind (known or unknown) intrusion and/or malware. Any other suggestions for achieving this goal would be greatly appreciated.
Take the computer, encase it in cement and drop it in the ocean. Seriously, it is unrealistic to talk about absolute security and safety against all known threats (let alone unknown threats).
Security is a process, and is always a balancing act between safety, risk and convenience. A good start is, as suggested, education as the key. Following good security practices such as many of the best practices listed on sites such as SANS and other similar sites.
Frankly (though there are those who disagree) I consider Skype a security risk in and of itself. Web based games are a great attack vector. Ensure Java is completely up to date as there has just been a major exploit reported.