Also should note this is Ontario

If the wall is anything but standard depths, you are making your own boxes. Not hard and pretty basic carpentry.

I would have hoped the installer knew that. I have no issues paying for the work to be done right. But the window sitting on the 2x6 framing by 1inch, Is that acceptable?

As long as it is affixed to the framing, should be fine. Doesn't need a larger bearing surface.

I would prefer to see a tighter fit betw the window and the framing, 1/2 max per side . I would also like the windows shimmed between the window frame and the rough opening where the screws are. I cant tell if they are shimmed and screwed in the middle, I would like to see that also. I think is especially importmant on casements windows since there operation is more sensitive to movement. If was me i would have either ordered the windows tighter or furred the openings out and would shimmed , i think they are be lazy and cheap.