You've got the basics right, but you're missing a key element of the equations. Turns in this game don't operate in a "traditional" fashion. On the surface, they do - the first champ to get a full turn meter is the first one to act. But where things get confusing is that thereafter, the person who goes next doesn't necessarily represent the person who has the next highest TM. There's a concept of overflow TM that dictates who goes next, and many of the CB comps that run on more elaborate rotations (2:1, or even 3:1) rely upon "cheating" extra turns by boosting TM above the boss, despite seemingly not being possible.
Most of this doesn't matter for you specifically - the 1:1 and 4:3 rotations don't typically require elaborate shenanigans. But it does mean that you can't just say "oh I'll make my champ X amount faster and everything will work". You very much need to use tools like deadwoodjedi to plan things out.
Specifially to your questions, 4:3 rotations are almost always used in order to get buffs to line up properly. They're almost never used for debuffs (though there are some very rare exceptions). This is usually because of a champ who has a 4-turn cooldown on a move, such as Helicath or Sepulcher Sentinel. Furthermore, the specific *turn* that the double-turn occurs is critically important. For Helicath, for example, you not only need the double-turn to happen on "turn 1" (aka the turn after CB stuns), you *also* need him to be last on his second turn, so that everyone gets full coverage of the Block Damage for both attacks. Sepulcher Sentinel, on the other hand, wants her double turn to happen on "turn 2" (aka the "middle turn"), and, again, she wants to be last on said turn, so that you not only block the stun, you also block the speed down debuff.
Speaking of which - two other critical elements for CB planning are handling the stun, and handling the speed down debuff against green CB. The former is usually done through a block debuff or a remove debuff - although remove debuffs are trickier because you need to ensure that the person doing the debuff removal doesn't themselves become the stun target. There's an entire set of rules dictating how CB does its stun targeting, and you'd do well to inform yourself on them. The speed down debuff, on the other hand, is simpler - you almost always need to just block it. The problem with the speed down is not so much planning around it - if it landed 100% of the time, you could build a tune taking it into account. The problem is that it won't land 100% of the time - even with zero resist, you'll still have a chance of resisting, and if even one person resists it, your entire speed tune gets thrown out of order.
