I kind of like this layout - how close can you be to a TV?? i wouldnt care but this is for movie nights too

How large is your tv? With the new televisions, the guidelines for size/distance from furniture have changed. The viewing point is much closer to the tv than it was previously due to the higher definition screens.

Our new tv has ultra HD (at least) resolution. It is a 77" tv. (which I was not in favor of purchasing - it seemed too large - the tv we currently had at the time was 55"). However, the only way that I would agree to a larger tv was if we purchased one that is very thin and sat flat against the wall + was able to display art (if desired) when not being used.

However, it's funny how you can get used to the change in size - we sit about 14 feet away from the screen - I don't know that I would want to be any closer.

Here are just a couple charts just to help with distance to screen size (your preference will be personal):

This graph below shows the optimal viewing distance based upon the size of the TV + the resolution:

The diagram below shows the ideal height of the tv + distance:

How high is your mantel? I assume that it will not allow for your tv to be placed at the best height level. I've never had a tv mounted over a fp - there are many people who do - but there are also many people who warn about the neck strain caused by having a tv that is mounted too high on the wall.

There are many styles of tv mounts that allow you to pull it out and down for viewing. Sometimes over the fireplace is the best place for the tv to live.

I do not understand the issue the ton of shelving is creating issues that can easily be solved by removing some of that and then decide where the TV owrks best If ateen hangout is the plan then ask them where and what size TV. IMO above the mantel is too high and it would nice to have the FP and TV both enjoyed when using the room

From your plan I see the main entrance into the room is from the front hall, so I suggest this idea. Float the furniture so you have a walking corridor for access to book shelves, door, etc. Position sectional with its back to the front hall. A sofa table, even larger than this one, would be useful and look great when entering the living room. T V over fireplace, two accent chairs (swivels would work best for your needs). With this arrangement I see seating for 8 and ottomans, tucked under the sofa table, could be emergency seating extras.

Ditto @RedRyder about the t v mount.

You can always mount a TV in front of bookcases