I don't know if this helps BUT we bought a MCM-ish house on an acre 2.5 years ago. The house was designed and built by a non-renowned architect in the early 60s. It is 4600 square feet. Out of the 10 or so houses on our street, a couple are smaller, most are the same and a couple are more like 6000-7000. Most people thought of the house we bought as a tear--down. We are just finishing up a to-the-studs remodel. We haven't changed the exterior much at all. We love lower ceilings. I would never buy a house with high ceilings. I especially would dislike an addition with too-high ceilings. 9' is good. We have a butterfly roof so part of our ceiling is 11'6" and I was really stressed about it. I'm only okay with it because it's mostly in public/non-bedroom area and at least some of the ceiling in our house is low. We would have loved a house in the 3500sq ft range. I think it's very very desirable. Add-on if it would increase your happiness while you live there, though. I will say that if you are interested in resale, many purists would have a problem with the addition no matter what you choose unless you are super super consistent with the rest of the house and what the original architect would do. We met with four architects. I would encourage you to meet with more architects! You never know, the right idea could really clarify things for you!

Keep existing structure, complete gut the space, new footer(s) inside existing structure, load bearing structure above those, floor joists above that, subfloor and refinishing. Have engineered plans/permits before starting. Basically an insulated and interior crawlspace below the new floor when done. Have access to down there, you could use it for storage also. Not impossible. Plenty of work but not impossible. Sounds like it would need a big reno anyhow from description. Just more work than a standard DIY gut and redo due to structure work involved. This is something a GC and crew normally does. This does give you a chance to make it how you want it. Hopefully selling price reflects the need for a large reno. what unexpected or nasty surprises did you encounter? I have found a lot of things in my current house where I ask myself, what were they thinking? So you will probably find a fair amount of stupid behind the walls. When I redid the drain system, there was an old 1-1/2" drain line from the kitchen that had so much gunk built up there was maybe 1/2" left for actual draining. Also the electrical was mix of grounded and ungrounded wire, and tons of junction boxes in the basement, I redid all that mess. Found a lot of the wire nuts where the wires were loose or arcing was happening and it welded the wires and nuts together, at least they used junction boxes or the house probably would have burned down... In laundry area, an ungrounded range receptacle was used instead of a grounded dryer receptacle even though the wire they used did have a ground. At the panel the fuse was rated at 30A so it was safe, just annoying I had to get a different cord to plug it in when I moved in. I eventually changed out the outlet for future owners... Oh yea that old fuse box the main fuse connection started arcing! Talk about fire hazard! So that was replaced with a breaker panel. Also in the laundry room the washer standpipe was a 2 inch that went into that same 1-1/2" from the kitchen with a vent tee instead of a sanitary tee... (so much fail). It now has its own vent and drain to the soil stack. Higher radon level than wanted, had to add active mitigation. Kinked gas line multiple places... Bath vent in attic went to above a soffit grate so 'some' moisture went outside but some got in attic. Not enough attic ventilation. Lots of other stuff, but cant remember it all lol.

Our neighbors have a large house with similar siding amd when they moved in they painted the siding white and the trim a soft black, kind of like what housaon posted. It took a few days to get used to since it is a very large house but it looks great now, very fresh and current and certainly less expensive than replacing perfectly good siding. they also refreshed all the exterior light fixtures to modern black fixtures which added to the overall modern effect. i think a simialr treatment would work well on your house. And I agree the shutters should go.

Useful comments coming in. Thanks. 1. The unit will be used for mom, but also may double as a rental, or place for my wife and I to retire as well, and maybe an AirBNB , etc... Yes, ADA makes sense. 2. ADU: Not sure if it was clear, but we are also trying to add on two bedrooms to the main house. In this case, does an ADU still make sense,? 3. I think HOA prevents a completely separate unit as well: "No more than one dwelling shall be built upon each such lot. " but I wonder if a breezeway solves this, however, the goal is to NOT have mom/tenants be able to have access to the main house. Wife does not get along with MIL.