Kristen,
Sorry for bailing on out the conversation yesterday. The sun was shining here (finally!) so the bosses closed the office at 1pm for sunshine liberty. It was great!
I love the color pallete that you like at Sherwin Williams! It's very, very similar to what mine is. My living room is done in gold, rust/red, green and dark purple (I have to have purple somewhere!). Believe it or not, our living room is 16x26 with a 14' vaulted ceiling, so I understand the hesitation in doing that much space. I thought my arm would drop off after washing the brown over all those walls! Needless to say, it took me awhile!
How about this? Use the sage green color on the walls and then the gold, or a lighter gold with the same tones, as the trim? I know the SW swatch shows the walls in the red/rust ciolor, but since your furniture is that color, you can use that as your accent color. If you click on their color planner (might take awhile with dial-up) and search for the sage color, it will show you a color pallete with green walls, a tannish/gold trim and teal furniture (planning ahead for your MIL's stuff!). That sage green is a really relaxing color - you'll be surprised at how warm it makes your room. And the gold will look beautiful around the window trim with all that light shining on it.
If you aren't sure, you can always do what I did. Buy quart sizes of the colors you like and try them out in small patches. You would not believe the array of colors splotches I had painted on my walls!!!! I thought my husband was going to throw in the towel.
The one other hint I'll give you is this: Trust your instincts. If you are being drawn toward a color, even if it's a color you never thought you'd like, try it. I am not a fan of yellow and I could not have imagined having gold walls. I don't even wear gold jewelry! However, I kept going back to that color time and again and when I finally bought some and put it on the wall it was perfect.
I hope this helps! Keep me posted!