From your description, I'm not clear on the layout at all...when you say put the tv in the small back room are you talking about the area in this room by the sliding doors? A sketch of the room with dimensions would be helpful, esp for you as you try to lay out furniture and need to decide what fits and what doesn't. I know you said you want a more formal area for when you host guests, but I think, given the toddler, you should start with function first. IMO, a house should give the most space to the maximum utilization. So if you will be needing play space and tv space which will be used on a daily basis, then that should take priority over a formal seating area which may be used less frequently. Rather, there are ways of combining both functions...keeping a play area with toy storage, perhaps by the slider and then incorporating seating and family TV time and entertaining around the fireplace. Regarding the windows, I would suggest that you treat the lower windows as you wish and ignore the upper windows. The vaulting in the ceiling has some odd shapes and some of the window placement is awkward, so I would ignore them ... pretend there is line going around the room where the lower ceiling is and don't decorate above it.

Eleven feet is plenty, so I would keep the sofa forward of the traffic path. I was thinking if your tv was above your fireplace, you would need 6-8 feet between it and your sofa (depending on the size of your tv) and wanted to make sure it wouldn't impede traffic to the garage. I like your mock-up and your enthusiasm! Maybe you have more space than I thought. Is it possible for you to post a picture with your sofa in front of the fireplace and your chair (or two - any chair would do for the second one) by the fireplace? Really, if you like the arrangement for tv viewing and feel there is adequate room to move around, it's a win. One thing to mention, some people don't like sectionals because they feel they are limiting in terms of rearrangement. We have one in our family room, but it works for our purposes. It's really a personal preference thing, and I wouldn't want to talk you into making an impulse buy. LOL

If you're willing to change the furniture, something lighter like some of the examples above would look so nice. Frankly I prefer the softer rolled arms because they're so comfortable and allow you to lounge around in several different positions, put your legs up on them, etc. Comfort first, I always say.

I like your current arrangement. For more seating, you can use two longer sofas in the same arrangement. Or a sofa with two chairs as you have it but without the ottomans. That leaves room for a backless bench type of seating to face into the conversation area that wouldn't interfere with the TV. With any options, your seating area is rectangular, so a rug would be fine to use. You may have room for a narrow console table behind the sofa facing the tv, if you place a sofa there.