Gil, took a peek at your saw; should work fine. Mine's a bit different; it's a chainsaw motor & body, but uses a diamond circular saw blade. The one your planning to use will be better than the type I have for this project, and I understand the availability of a cutting service may be limited.
I assume your planning to take out the entire wall from footing to mudsill (flat 2x8 on top of basement wall), then use a steel I-beam or wood header. Often you would cut your opening oversized to accomodate jack studs to support a header, but with this type of saw, you could also cut pockets on each side to accomodate a bearing surface. I think I'd just go oversize if I were using wood, but might do pockets if it were an I-beam.
Beforehand, be sure to construct a temporary support wall close behind the wall to carry the load of the joists and structure while the concrete is removed. If the joist are parallel to the wall your cutting, it's not as critical, but I do think I'd put in something to be on the safe side. Also possible in this case would be to structurally head the opening by plating the rim joist (outside joist) overhead with a couple more joists the same height; this could be done before cutting and delete the need for a temporary load wall. You'll likely also have a foundation bolt or two that will first need to be cut off at the top of the area to be cut out.
Once the slab is cut free on both sides, you'll want to toss a few old tires into the pit for the slab to fall on when you push it out; this really helps in facilitating breaking up the piece and removing it. If you have a fair size tractor, you could saw the fallen slab in half, then saw a hole in each piece which might let you chain onto them with the tractor for easier removal. Use extra care in cutting the slab after it's down; it may want to tilt at the cut and bind the saw.
To make room for the slab to tilt out without damaging or binding on framing, you'll probably have to make a series of short vertical cuts at the top (6 to 12" a foot or less apart), then bust the pieces off with a sledge.
This will also show you where the vertical rebars are; measure their locations and transfer them to the bottom of the wall near the floor on the inside. After the sides are cut, you can cut horizontal slots at these points (from the inside) to sever the verticals; this will help the slab come loose without damaging the footing by having the verticals try to bust free with the slab. Once the slab is out you can cut off the remaining stubs. Be VERY sure everyone is at a safe distance when that slab goes over!
Back to the drain tile; you'll want to sock the tile with something like a woven weed barrier, then surround the sides with 6 to 12" of coarse sand or chat gravel. If keeping the tile level means it will be flush with, or slightly above the top of the footing, don't worry about sand/gravel on top of it. If it's slightly below the footing top, bring the sand/gravel on up level with the top of the footing and over the tile. Cover the tile and gravel with a 6mil plastic sheet before pouring your landing.
Gil, that pretty much covers what currently comes to mind; feel free to ask further if you need to, and be sure to let us know how your project goes!