As an operator type, Casement will generally be tighter than sliders and/or double hungs. If you are worried about stiff breezes and drafts, I'd probably look at those first.

How about mimicking the window to the left of the door - two casements and a fixed in the middle?

I would investigate this product for your porch

https://ezebreezehome.com/

We are in the Upper Peninsula of Michigan and it can get 20° below with wind chill. Are those porches insulated?

I guess You need to do your own research on what your enclosure needs to provide and how much that will cost. No reason to insulate the porch if all the cold will transfer through the slab. How do you plan to combat the cold.?

To start a 4 season room in Canada has to be an actual addition not a porch closed in very much the same climate in many places here. Waht do you plan to do in there in the winter ? NOt sure about nthe codes where you are but you need to find out . That space will be cold as heck unless you find a way to keep the floor from freezing .

My contractor is going to dig up the existing slab, insulate, and extend the in floor heating that is in the house.

The space is only 112 sq ft so I’ll have to see if the cost is justified.

So extending infloor hesting is going to be a JOB the foundation needs to be just like a house and that needs to be shecked for code . IMO I would leave it as a porched screened and use it for as long as possible each year 112 sq ft not worth the expense that is my thought .If you go ahead ans do this them IMO the windows need to be a perfect match to the ones on the left