Brice, a huge Welcome to FOG!
I believe you will find that Kapex extend behind the fence less than any other 10" miter saw, so that aspect of using your current bench should be no problem.
Probably one of the on-line dealers could provide you exact measurements. All of my Kapex are at my shop. Tonight I am out of town.
Your best Kapex dust collection will use a 36mm AS hose, with can well be arranged to reach a Festool CT without needing any extra space behind the saw. We have just switched one of our Kapex from using a dedicated CT22 to direct connection to our shop DC system, with a 100mm pipe coming down the wall behind that Kapex. There is a Y-sweep on that pipe. One branch serves a reducer to the 50mm end of a short 36mm AS hose for the Kapex. The other branch of the Y serves a typical miter saw dust shroud. We have always used that shroud. That combo provides excellent dust collection. So far using the plant DC is working as well as using the CT22. The advantage is this way we use fewer bags. If this system proves out in the long haul we will do the same for the Kapex on the other side of our shop.
Best of good wishes.