What about removing old configuration files and directories? Does apt know what files/dirs an app creates, and can it remove them?

How do I know which packages are necessary?

What DE do you recommend for a netbook with 2 gb ram and a single core 1.6 ghz processor?

What if I want to get rid of a DE altogether and learn to do everything via terminal, what do I delete to accomplish this?

I am into emulation, reverse engineering old video games, and I'm an ok Java programmer. I'm somewhat clued in to this stuff, just never bothered to learn before. I might need I think X (?) to run an emulator and web browser, but I want to delete everything I don't need and cook my own tools when needed. Yes this is insane but I'm stuck with a netbook for now so I may as well optimize for it's limitations.