We recently bought an early 80s ranch home that came with carpet everywhere. Including bathrooms. So, naturally we've ripped all that out and are planning on putting a wood floor throughout the entire main floor (aside from the bathrooms, which will be tile).

The subfloor of this home is two-layered with the bottom layer being made up of 1/2" plywood. The top layer is 3/4" plywood in about 1/3 of the home and particle board (not OSB) in the rest. This is both glued and stapled to the lower layer.

Given the makeup of the subfloor, it seems like our best option is to float something on top of it. My wife and I have found an engineered wood floor that we love and are planning to go with that, but the real part of my dilemma lies with the open staircase in our home.

Near the front of the house, there's a staircase to the basement with 3-open sides. These sides have a sill-plate that's flush with the subfloor and posts/balusters that are mounted to the side of the landing. We plan on redoing the railing with something a bit more modern (maybe cable/rail, or something).

So my question is... how would you lay engineered flooring around a staircase like this? Especially when floating.

Would you attach stairnose to the subfloor and start floating (glueing the tongue/grooves together) from there? This would effectively make the floor not-floating around the staircase... Could this present any buckling issues in the future? I know that engineered wood is less susceptible to expanding and contracting, but I dunno by how much. I'm also not sure how this would be any different than if we were actually attaching the entire floor to our subfloor. To me, this seems safe-ish.

Otherwise, I suppose we could build up a sill plate around the staircase that has a notch routed out of the bottom for the floor to float under...

Or we could bite the bullet and rip out the whole subfloor and install plywood... but we're looking at 1,500sqft of floor, so I'd really like to avoid doing this.

Any professional thoughts would be extremely helpful! I've installed nailed down hardwood flooring, glued down engineered flooring, and floating laminate flooring, so I've got some experience with flooring, but have never been in a situation like this.

You could stop the flooring with a bull-nose reducer, like for a sliding door. The balusters will still rest on the plate, which you could cover with a ¾ X 6 inch stair nosing. The bull-nose reducer will meet the edge of the stair nosing and you can drill new balusters into the stair nosing or run your cable to posts. If the matching bull-nose reducer is not available, you could rabbit the edge for an expansion gap.
Finishing the stair nosing to go with the laminate would be your problem.
Sand with a random orbit and ease the edge to meet the laminate trim, or to finish the edge with the rabbit.
A piece of molding to go under the nosing projection will cover the plate that shows under the stair nosing.