Powermac G4 Help

Hello! My mom wants to give me her old Power mac G4 (Quicksilver) desktop if I buy a monitor for it. I'm hoping to buy the matching monitor that pairs up with the system. The reason I want to buy the original monitor is to be safe and sure it works, and the other reason is because I see people selling it cheap from $60 to $120. Where can I buy the matching monitor? I was also wondering if there's a specific microphone that can go with it. I checked all sides of the system, there's no microphone plug thing. Is there maybe a USB microphone, or are some headphone sets with microphones compatible, or what? Where do I get THAT? I'm a gamer, I know I should be using something like a windows system, but I also like to make digital art, animation, etc. I have more abilities using this desktop. These next questions are about the software: What is the highest Mac update it can go to? Is it only Tiger OS X? Is it possible to put OS X Mavericks or the upcoming Yosemite on it, or is it outdated? Since I'm a gamer, I have no idea if it can even use java. If it does run java, can it go up to 64-bit java? I know I have the keyboard, mouse and speakers, but can the modern accessories work, too? Thank you if you have an answer!