Trouble

That doesn't look too complicated to me. Ask the carpenters to drop that window at least a foot to give you at least a little challenge.

Use a larger than normal tinner's wing on the corner and I'd make the steps 8-10" wide assuming th erock go to the deck. Were the carpenters smart enough to slope it away from the wall like a cricket to help guide water from the wall? If not, I'd put a flat piece of 6" I&W at the wall, followed by a 12", an 18", and even a 24" piece. Then, if you want, run a 36" to and up the wall. Then add something under your through flashing to go over it AND your flashing. This is SBS, but the theory is the same. The water runs away from the wall. Every little bit helps.