Yups, that's the basis of the Ninja vortex. 123 and Ji1. it's beautiful, Ji1 provides a higher damage combo than J3, at the cost of some range.
F23 I prefer 32. On block, 32 is safe. You can just end there, or go into sword spin for more damage.
If they get hit, you can do 323, 12 xx Machine gun for 29%
32 will stuff even the fastest of reversals, but the perfect timing can be tricky.
B1 can miss if the opponent moves back and they're too far away. B2 is great though.
From what I know, only certain characters back dashes work. I have to do more testing. Even then, it's a guessing game considering only BACK dashes have invincibility. They have to guess which side you'll go to, otherwise they'll accidentally forward dash into your Ji1.