Hi, A good way to start is to draw a scaled floor plan of the space. When you see furniture that you like, you can then cut out; also to the same scale, the basic dimensions. This will make it easier to assess the foot traffic around the room and furniture layout. You may find a modular to big and limiting to layout. Maybe a sofa with 2 accent chairs (not necessarily matching) gives more possibilities. Also consider which direction the room is facing and what light it receives, this may also help with layout in terms of the TV, i.e will the sun shine making it hard to see the screen. Hope that helps.

In any event, I think the upper half of brick cavity where logs are stored could be modified and used as a place to mount your TV. I'm thinking some sort of structure could be built into the cavity and the TV mounted to it. This would require the services of a qualified carpenter to ensure the entire structure is properly and securely anchored to the brickwork, and to ensure it can support the weight of the TV, especially if a pivot mount is used. Barring this idea, is there adequate space in the opening between fam rm and kitchen/dining area which could accommodate a purpose-built unit for your TV? In other words, built directly to the right of the brickwork?

try mounting the tv on the same wall, add brackets to secure any cabinets to the wall and toddlers are usually OK with stairs after you teach them to go down steps on their bottoms

Maybe something like this. Tv unit on the long right hand wall. Then lounge facing that with accent chairs either side. You could also have a long 4-6 seater modular sofa, you have the room. I have shown a 8 seater rectangle dining suite. Just make sure your lounge furniture is away from the walls to allow for walking circulation.