For the j.BC j.66B dj.BC, the important thing is to keep them low and close. The way I do it is 2C (delay as much as possible) 5C j.9B(2)C j.66B dj.BC. Honestly, I don't see this as being worth it. If you're after carry, just do dj.BC dj.66A, which I find much easier. Damage isn't exactly something to write home about either.
As for the 22C stuff, it's only lower than doing the 5BB combos normally. You'd usually have to do the special neutral super jump cancel from 5BB. That means you airthrow from higher and land slower. With this, you can do a normal jump. As for why you'd do a 5BB combo in the first place, it's so you can do 5C 2C instead of 2C 5C, which does far less damage.
EDIT: As for blockstring enders, whiff a 5A. CNana has a lot of moves that move him forward. Good blockstring moves are 5B, 2B, 5C, 2C... Meaning ALL YOUR MOVES. Do stuff like 5CA, 5{C}2B, 5A6E, 5B[B]22C, etc. CNanaya blockstrings are the hardest to learn 'cause they're so good. You have so many options that it takes a lot of experience to know what to do in a situation. In general, you want to whiff cancel (or 22C) your slow normals and get back in there with a 2B, dash, IAD, etc. CNana pressure isn't really a high/low mixup game, though, so don't feel like you have to throw an overhead every so often. It's more of a "I hate this game" type of pressure, 'cause you stay in there with frametraps for hours.