Creating a water break on flat concrete

We have a covered breezeway between the house back door and the garage. The back of the breezeway is closed, and we would like to close the front to create a mudroom. The challenge is that the breezeway floor is the same level as the flagstone patio area next to the driveway. I would like to create some sort of concrete water break, and build the wall/door on top of that. Here's my plan:

Create 2x2 form where new wall should go, pour concrete along the entire length of the new wall. Attach pressure treated sill plate/wall on top of this new concrete "ankle-wall." Etc - easy enough to finish with wood/plywood/tyvek/siding from there.

Questions:
- Is a 2x form (1.5" high) good enough here? We never get any standing water in this area, I only expect rain splash.
- How to ensure good adhesion to existing slab? I plan to clean thoroughly, but is there some sort of bonding primer made for concrete-on-concrete? Can I pour the new concrete over partially-sunken tapcon screws to hold it down?
- How best to fix the PT sill plate to this ankle wall -- tapcons, wedge bolts (worried about cracking the ankle wall with these), construction adhesive, or other?

Thanks in advance for your input.

Todd