For me, my interpretation was to focus on the elegance of the era and that involves a lot of "stuff" (I can see MrsFlynn cringing.)

Everyone has a different design esthetic and in real life I'm a designer and builder at heart and a collector in fact. You could say my many real life homes are not exactly what you'd call minimalist.

I see you have no problem using CC. I have a serious CC addiction so my builds are loaded with it. I think it adds character, but that's just me.

The large living room needs a "quiet" space in the front. A reading area with an elegant bookcase and cozy chairs, maybe a chess set. I'd place a sideboard with some candles and ornaments. I think I see where a grandfather clock would go.
Using MOO you could double up one of the long tables and create a very formal dining room with a china cabinet and a couple of sideboards.
MrsFlynn suggested a butler's pantry in the kitchen and that's what was on the original plan so I'd fill in some of the kitchen space with that. I'd also put a couple of cozy chairs in front of the fireplace in the kitchen.
On the original plan, the room behind the livingroom shows a back-to-back fireplace and you have lots of room in there. You can eliminate the chimney on a second fireplace by using MOO and in "buy" mode, use the hand tool to removed pieces of the chimney. I'd make that a family room with couches and a tv.
Because I made my house smaller than I'd have liked, I eliminated the closets upstairs. I just realized I didn't get many pictures of the upstairs. My suggestion would be to eliminate the chimney piece that is plugging up that one bedroom unless you want to keep it authentic.

The room in the back corner on the right is actually a screened sleeping porch rather than another bedroom. Lots of room for a study up there.
And in case you hadn't noticed, I tend to get a bit carried away....
Edited to add: Maybe you aren't using CC and some of the objects you've used are from different EPs or SPs that I don't have. My apologies if that's the case.