The plan separates each living space with access from a central hall. It would work well for an office building but not so much for a house especially f you plan to entertain. I find that trying to make a good plan out of a bad one is usually a waste of time and effort. Its like renovating a house that hasn't been built yet. Decide what you think an entertainment space should look like and develop the house around it. But I would not design a house around an occasional use. The interrelationships of family members should be the dominant theme of a house. And I would never put a level change in a living space unless there was an alternate wheelchair route. If you plan to entertain, the front door should have wheelchair access too. An accessible half bath would be good too.

Put the clock over FP. New sofa and chair with round coffee table. Tall floor lamp next to blue chair and angle the chair and turn. I will show you an inspiration visual.

Really nice room. Looks comfortable and inviting. Good choice w/new sofas. Like the fireplace as is ... but less clutter could improve the look of it. Not sure what the picture is above the piano. If it is a family photograph, reframe it and the family photo on the mantel with the same frames and put both above the piano. Really like your coffee table. One day it will be a valuable antique if you don't booger it up. So, for the coffee table, consider taking the table to a glass company and having a dark gray tinted thick glass top created for it -- no refinish for the table necessary. (Alternately, cover everything but the top and paint the top only -- perhaps black or else the same white as your cabinets.) Do the same for your current end table as you do for the coffee table. If you're going to add a second end table, since matching the existing one would likely prove difficult, consider a totally different look -- perhaps a wood 2-drawer filing cabinet? http://realsolidoak.com/office.html

Don't have time to answer all of your questions but here's what I can suggest: 1) Lower the mantle on fireplace a little, as well as the painting in the niche. (See #2 here) Consider changing the mantle to something less rustic and paint in color A (see next suggestion) 2) Open spaces should be cohesive - which you can easily do with paint. Choose 2 colors or 2 shades of the same color and vary placement in different areas. (see #5 here) Consider adding a simple chair rail to the dining area. For example, with minimal effort, you could use color A below the chair rail in dining area, as the dominant color in window treatments fabric (I"d use draw drapes) , the back wall of niche, throw pillows, lamps ac, and maybe an area rug in living room, and in accessories (see #3 here) in living room and kitchen. I'd consider adding some of that color to kitchen also -- back of open cabinets for example, recovering bar stools and dining room chair seats to match drapery fabric and possibly slip covering one of the armchairs in the living room in a pattern that incorporates the wall colors with other colors in the space. You want to use coordinates, not just the same solid everywhere so look for different textures or patterns to add. Hope that helps. I've inclluded links to additional info about topics I mentioned that I think you'll find helpful. 3) see #2 - I'd choose lamps with either a base or shade to match color A. (See #7 here) 4) Add plants. If you aren't there often enough to take care of them, use artificial greenery.