1. Yes but sometimes when you do the collider whiff they fly behind you or further away, it depends on how close they are and what normals that are used it seems, just roll with it.
2. Just gattling it, from normals, 5A>6B, 5B>6B, 5C>6B, and 6B>6B are all examples of just mixing them up.
3. Not character specific, some combos proration makes doing AC whiff>6C harder than normal or just not work, GF whiff remedy this.
Outside of pull and recovery on the 2 moves there isn't much of a difference.
Ah I forgot that GF whiff can only be used after a sweep or something that puts them in a OTG state.
4. You just can't do the back dash you have to time it.
Now when it comes to Air dashes you have to more less react to it or look for the time they will use their j.C.
It's all in the timing.