I actually like the arch and brick detail, although I do understand houssaon’s POV and it’s good to see different possibilities. I think I would keep the brick arch and restore as much brick as possible and maybe bring in a bit of wood detail, also. Is you would like to see how different ideas could work on your house, I recommend this company. https://www.houzz.com/pro/uoflcardfan77/creative-visual-concepts-kevin-strader

I don't care for either one of these mirrors against the stone. Unless they reflected a fabulous view or chandelier I wouldn't do that. I would try to come up with something unexpected. We don't know your style, so it is hard to suggest the right idea. This ladder vignette made me think of a big antique ladder with some interesting tapestries folded and hung over a few of the rungs. Here's a variation on the horse idea.

My husband and I are currently working with architects to design a home that is very similar to what you've described (1.5 stories, 2 bed, 2.5 bath - one tub, one shower). However, in order to accommodate our needs (a study on the first floor, a pantry, etc.) we ended up a little above your stated size preference (1700 square feet). We've been cautioned against building small for some of the reasons mentioned here, but honestly we would pay more for a smaller home. We'd prefer a small place with high-end details to a larger home. In the area where we live there are not older homes this size on the market, although we waited for about ~2 years seeing what would come available. Ultimately, we decided in our area, which has a high percentage of retirees and child-free couples, a smaller house could sell if/when we have to. But more importantly, we didn't want to compromise on living in a house we didn't like trying to anticipate market trends 15-20 years down the line.

Iowa, you must have a basement and returns could be "easier" to relocate. Hopefully, those are just returning the CFM required for that room and not the entire house. Be aware that with 18' walls there will be blocking somewhere above those vents or something framing in from whatever's on the other side of that wall which might prevent you from raising the vents up higher (at least easily). A well-advised HVAC designer (not equipment tech) can review the size of both stud space openings through the floor for each vent and possibly find another location/combine a couple if you can meet the CFM flow. The location to the left of FP is too close to the floor register IMO anyway.