As to your other questions, I did not take the time to look at your ebay links.
Why? You need to much more research yourself before buying too many things. You don't yet have enough understanding what to buy and why.
For example, your link to the processor is for an AMD. No, you cannot use that with your Mac or any Mac ever created. For older Macs (PowerPC) you can only upgrade using processor upgrades made by a few specific manufacturers that make Mac upgrade processors. Some examples include Sonnet, OWC, PowerLogix, FastMac, and Gigadesigns. A good place to go to get an idea what upgrading a G4 would cost would be here:
http://eshop.macsales.com/MyOWC/Upg...ype=Processor&TI=5455&shoupgrds=Show+Upgrades
(but keep in mind that every model of G4 is potentially different. There are families of the same type but the upgrades are not necessarily cross-family compatible) To select your model, go here:
http://eshop.macsales.com/MyOWC/Models.cfm?TI=5619
And you do not get automatic increases in performance based on clock speed. There are too many variables for that.