1. If you are in the middle of the screen where the 2nd hit of 214B won't bounce them off the wall, I don't think 236A will connect. Usually if you're in the middle of the screen, isn't it supposed to be 214B(1) > 236A > [i'm gonna assume 6C > 632146C (if you have at least 7 Magatama]?
2 & 3. There's a strict timing to linking 2C [did you mean from f.C?]. To do falling j.C, you have to recognize the lowest point that Haku can be in midair, and still do a j.C without it being interrupted from landing. Once you link 2C to a combo, you need to be aware of your hand/thumb placement. 2C is jump cancellable, so during its animation, move your arcade stick and/or analog stick to the neutral (5) position before you input a super jump.
* So say, your opponent is in the corner already (I'll write out the numbered positions I move my stick):
6C(full) CH (close) > 214B(1) > 41236C > 2C[369] (jc) > 2C (j.2C) > 5C (j.C) > land > 2C[52369] (sjc) > 2C (j.2C) > 5C (j.C) ~ approx. 7284 Damage; requires 5 magatama