depends on what you want to do... Personally I deal with my sources as a whole disk. So when I rip the dvd, I import the whole dvd (either via avisynth or convert it to lagarith/huffyuv/utvideo). I've done the clipping method before also. Just depends on what you think is better for your workflow. try both out and decide.
Your friends are also wrong. cleaning and preping isn't the most important. It's definately something you should pay attention to but not the most important. Since you're just getting started, I would completely remove "cleaning" out of the equation. At most you should be deinterlacing and/or IVTC your sources (if needed). Read up on the guides we have about it. After that, just start editing. If you get too hung up on trying to learn how to clean your sources and whither or not you should be clipping or editing whole episodes, you'll overlook the more important aspects of the hobby, which is the editing. You can have the best looking source but if your editing sucks, its not going to matter
Hope that helps.