Yeah these are in DMC4 too they are called Combat Adjudicators and found throughout the game. As you get further they require longer combos until you eventually get to SSS ones. They do not halt progress but usually conatin nice goodies like Blue Orbs to increase health bar when you get 4/4 of them.
SSS is only possible by switching styles and upgrading Dante with new move/style sets.
3 is the best out of 1,2,3 =) hardest as well. i just beat virgil so im not that far ahead of you. currently inside the leviathan. but imma "get" the full version because i want all the cutscenes and such.
I don't know. I've only played 1-3, watched the anime, and played the demo for 4 on my friend's 360. I'm waiting on the PC version to get released so I can actually play it as my friend won't be buying the game. Besides, I still need to finish Assassin's Creed.