Double-tap 6 to do a quick dash forward.
Double-tap 4 to do a quick dash backward.
Double-tap 3 to do a quick crouch-dash forward.
Tap 6 twice and then hold down on 6 to sprint forward.
There are two ways to approach grapplers. If they are using throws, then you should strike more, as you cannot be thrown when performing a strike.
If they are using Offensive Holds (special "throws" that go through strikes) then you can use a normal throw yourself, as throws beat OHs.
Keep in mind that standing throws cannot grab an opponent who is ducking, so you can also duck to avoid most throws and OHs (though this will leave you open to crouching throws and crouching OHs, should they choose to use those).
Power Launchers will launch the opponent high enough that your most damaging juggles will be possible from them (and they also deal more raw damage than your average launch). But, the difficulty in executing these combos varies greatly from character to character. So bottom line: If you can reliably do your high-damage Power Launcher combo, do it. If your execution skills are not good enough, stick with your BnB combos.
Power Blows can be more or less efficient than your character's max damage juggles, depending on the weight class of your opponent, the environment, the juggle potential of your character, etc. In general, they are pretty useful, however.