Rest--people training for hypertrophy and endurance tend to use shorter rest periods (30-90 sec?). Those training for max strength tend to use longer rests, basically until they feel ready for the next set, even if that's 6 or 8 minutes. This is something that will be more clear with experience--make a plan to try for a while, then vary it and see how the results vary.
Confusion--that's common. In fact we're all confused most of the time! :) There is a lot of information to absorb. Sometimes we give advice using terminology that has a clear definition in training circles, but may not be clear to a someone new to training. And exercise is a really complex activity, and discussing it can get complex. Nothing makes it all clear as much as experience. If you train faithfully, keep thinking, read a lot (and try to sort out which writers to believe), a year or two from now things will be much more clear. Not absolutely clear, but more so.
Changing--you don't have to reinvent the wheel each time. You don't have to change your whole routine. Like Kenny said, just try a different flavor once in a while. It doesn't have to be exactly 6 weeks, although many of us plan our training in 4-week or 6-week blocks, so something like that is convenient. So if you have been doing flat barbell bench for a while, you might change to incline or decline bench, or dumbbell bench, that sort of thing. Or just change your rep-set scheme (how many sets of how many reps). You might just change a couple of your lifts at a time, or sometimes change more. As you gain experience this will become intuitive.
You misquoted Kenny. You said "heavy, normal, easy". You don't get it. A light day isn't easy. It can be every bit as difficult as a heavy day. Heavy, moderate and light refers to the bar loading. Study Matt Zito's training log for an example. You'll probably use less volume on your heavy days, more on your mod days, and even more on the light days. So on your heavy day you might do 3x3 with what is for you a fairly heavy weight. The first set will be fairly east to complete, the second will be tougher, and on the last set you'll feel like after the third rep that you could get a couple more if you really grunted it out, but don't grunt it out. On mod day you may do 5x3 with somewhat less weight. The first set of 5 will be fairly easy to complete, the second harder and on the fifth rep of the third set you'll fell like you could get a couple of more reps if you really grunted it out and allowed form to slip, but don't do it. On light day you might do 3 sets of 10 with even lighter weight. The first set will be easy to finish. The second will be harder. On the third set those last few reps will be pretty tough because you will have completely depleted your energy. By that last rep you'll fell like you could get one or two more reps if you were willing to let form go and really grunt it out, but don't do that.
In your post when you mentioned heavy day you said "Push self to maximum, reach failure, rip body apart, go home with a smile." If you do that very often you'll wipe yourself out in a hurry. This is a marathon, not a sprint. Train in a way that you can sustain for a lifetime, not just for a few weeks.
Having said that, on your isolation lifts or accessory work, it's not such a big deal to go to failure more often, it won't take as much out of our CNS as it would on the compound lifts. Here's a useful article: http://jasonferruggia.com/training-to-failure-part-1/
Here's part 2 of the same article:http://jasonferruggia.com/training-to-failure-part-2-lessons-from-the-old-school/
So most of the time you should be leaving a little in the tank. Never go beyond what you can do with good form, except on an occasional max test. Even then, if you've been training with good form, it won't slip much.