Put the tv in front of the rear windows. Put the 2 seater in the middle of the room facing tv near fireplace. Coffee table between tv and two seater. leave the 3 seater on the same wall but closer to pianos current position. Put piano in suggested position. As for the bay windows a nice small round table with two chairs. A place to sit and have a drink and listen to music and look out the window...adds intimacy.

I think the design of the exterior has real 70s integrity. A bit of paint is all you need. Replace the garage doors with floor to ceiling windows matching the aesthetic the current windows already have. You should check out Cocontest.com for architecture work, or you could try and find an interior architect (there are degree courses in interior architecture these days) I've seen loads of one plan's posts and it would definitely be worth having a chat with them. I also think that you'll get more out of the project if you can educate yourself a little on design. I do my best to do this over on www.houseplanshelper.com

It feels bland because floors and walls are beige. (ish). If you want to make a statement about a room. contrasting shades work really well. You have spotlights so the south aspect is irrelevant. Put a dimmer on spots if not already there so you control the light and feel of a room. I presume the fire is staying there so that back wall would be perfect for TV to be put on/entertainment system. Corner couch facing tv wall with chaise lounge on fire side. Behind the corner or L shaped couch, table and chairs so the room is functional for entertaining also and the layout is proportional. The room also has a focal point (TV)

Could you hang the mirror on the back of your door? You may need to get stronger hinges to cope with the weight. As for paint for the drawers, either the same colour as the wall or the colour of your existing furniture and decorate as the previous commenter suggested. God luck with it. By the way . . Very neat bed-making there .