Any suggestions on how to lightly sand and poly it to enhance?
Not sure how bad the hardwood floor is there. You can rent a belt floor sander OR you van use an orbital sander and take off the sheen of the floor. If you are talking about a small spot then hand sand it. Vacuum up the dust. Use a tack rag to get the rest of the dust.
I use Mimwax Spar urethane for hardwood floors. It's the hardest finish other then Gym-seal which is used in the schools gyms
This comes in cans or spray. Some times I use both. I use can first then use a spray to "feather out" the new to the old in that different sheen look of aging
Do you have a link so I know visually what you're explaining?
The link I have is in my head. This type of re hap is not normally illustrated. To help get this in your mine keep thinking the word "nailer" to attach the steps too. Its basically a box in a box telegraphing in scales and thickness.
Lay this out from the top down. Another words figure what the threshold you use there will cover in depth and decided of you want that threshold edge to be flush with the new 1by oak riser for a finish or bring that out more to show a small or big tread that's flush to the hardwood floor height. Don't really look at this as building stringers. You only have 2 steps and one is actually the house floor joist that needs to look like an oak riser. Finish that first then lets actually build "a" step. You need nailer's for that for the tread and the riser and the side oak finish boards to nail into something.
To build that use a ripped down 2x6 and make a box. The height of that box will be less the thickness of the oak tread. Now lay box against the finished joist band that has the new oak fake riser. Nail that box trough the oak riser and set it. Scab a 2by laying flat inside the box against the porch floor. Side nail the front of the box to flat 2by. Now you have a complete frame to add the oak side finishes and also a nailer for the tread in the back and front.