The potential problems with removal of runner are dependent upon how the runner was installed. Some dearies actually tack the runner to the steps, tread and riser. Ouch, because removal leaves those holes to be filled and stained to match (very difficult to conceal). An alternative method is to use carpet bars which come in wood or metal, in an assortment of finishes. This is slightly more expensive but imo, also *looks* more luxurious. The carpet is barred at the back of the tread where it meets the riser; best practice has the runner tacked beneath each tread rather than slanted from top-front to the back of the next lower riser. Note that under-tread tacking also uses the most running feet of carpet, so the most finished appearance is going to cost. There are several other methods, so discuss intent with the installer before s/he does the work. One thing for sure, is to not use any sort of sticky-back tape: it either doesn't hold well, or holds too well and removel is labor-intensive. Because of the carpet pile height, if possible choose treads that are slightly deeper than usual so as to maintain fully safe depth.

I think it looks good black, without the carpeting on that bottom step❣️

No that would be okay since it is consistent flooring in the rooms.

I did a quick google of "central Iowa wool carpet dealer" and a bunch popped up. From big box stores to individual dealers of floor materials. So I think you might be able to find something in the center there. You might need to comb through a handful of places to find ones that deal in wool. One came up for me that is more to the East of the state (Iowa City) that looked like it has a bunch of wool using their search real quick: https://iowacity.abbeycarpet.com Oh, and I like that tile you picked out!