You do not gain any meter on hit or on block from landing EX moves.
The blockstring j.CD, c.C (2 hits), f+A, hcf+BD, cr.B, s.B, s.D, qcb+A does a bit over 90% of the guard gauge. It's pretty solid for guard crush, but it builds so much super for the opponent that you'll get C+D countered very easily. Seems to me that there's not really much of a gap between hcf+BD and cr.B, but opponents could get out of they have a 1-frame grab like Kensou or Clark, etc. Still a very solid guard crush string. It works midscreen or in the corner.
The hcf+BD itself cuts off about 40% of the guard gauge and is completely safe. Seems to be +0 on block.
If you do use it for a guard crush and it crushes before the last hit of the move, the opponent becomes launched. You could turn this into a big combo with dp+A [DC] hcf+B [Brake]. This only works in the corner. Feel free to use it against grapplers, just be aware that if you try anything besides jump or C shoryu you'll be vulnerable to grabs.
As for Zan-ei Ken, the recovery of the A and C versions are virtually identical, -4~6 it looks like, but the startup of the A version is significantly faster. On block you cannot be punished by most characters, but by some. Shen comes to mind with EXDM, or Iori's EXDM. Basically it's too far to be punished by normals or grabs so opponents need a far reaching move that comes out in under 4 frames. EX Zan-ei Ken seems like it's -1 on block, cannot be punished by anybody as far as I know.