Bricks, Masonry, Asphalt and Concrete - Flag over new concrete porch and pathway

I am reinstalling a concrete porch, and pouring a new pathway to it, as a base for installing square cut flagstone in mortar. We are re-using the 1/2" rebar from the old porch and adding wire mesh and new rebar. The base is tamped crushed stone. Should we isolate the new porch pour from the existing 3 brick/masonry walls of the house? Also, I understand that the concrete should be scored after it has cured, in order to control cracking, but.. won't any cracks that occur just be transfered to the flagstones? especially since there will not be any one continuous mortar line accross the surface of the work. The pathway will butt-up against the ashphalt driveway for about 16'. I plan on straight-cutting the drive for a clean edge, and we have built a form on the opposite side. Can we just pour up against the earth and ashphalt? Should I use 6mil. polly against the earth. I can't see how we can build a form on the driveway side and be able to remove it after the pour? We live in Toronto Ontario, freeze thaw conditions. Do we order high psi or air entrained concrete?
Thanks, Phil
What a great forum!

I would not tie the walk to anything else, to avoid problems with movement. The score marks do serve the purpose of letting any cracking occur where they are rather than randomly otherwise. Plan ahead as much as possible and align the joints in the flagstones over the cuts. Usually the scores are made every 12 feet or so. With the random patterns of the flagstones, the stones may not crack with the underlying concrete even through the concrete cracks at the joint. Usually, these cracks are minimal, not heaving.

To form at the driveway, insert an expansion board and leave it after the pour. It will be a form and allow for expansion. 6 mil poly will keep moisture from migrating into the concrete from the ground. This should help with freezing and thawing stresses. I would ask your ready mix supplier about which mix is appropriate for your project. We don't have really cold weather here.

Hope this helps.