To my knowledge the wall splat happens on St. CD to grounded opponent, regardless of distance to corner or screen edge. The animation looks like wire hits from XI but completely horizontal rather than angled slightly up. Also
https://youtu.be/OPalvVq9URU shows the screen scroll further back after Kula hits the wall so it's likely like XI wires but leaves the opponent in a crumple state for follow ups.
Of the three things I asked I'm most interested in the first, it would potentially make wall to wall combos much easier and reverse back to the wall situations with good reads and some meter.
That isn't to say the others aren't important. Linking a Cr. B to a St. A is pretty common so rush may become a great tool for confirms into BC combos. Take previous versions of Ryo for example, in many games he's able to do Cr. B, Cr. B, St. A combo, if rush is BC Cancelable he potentially has a 5 hit confirm to Max mode combos. That could be a way to ease newer players to other more powerful combos as the two extra confirm hits are likely to scale the combo damage.