What country and state are you in? That will affect whether you need a fireplace. I like freestanding bookcase/storage units, they must be attached to the wall if tall and not deep. If getting custom built get at least 3quotes. Finally, there are DIY shelves available at hardware outlets and stores like Ikea.

Not for me, I find the concrete floors too harsh, the one good thing about them when they go off trend easy to cover with something else.

any gas log fireplace should have very specific instructions for safe installation with measurements for distance from back and side walls, height above floor and height of any mantlepiece above the front of the heater and details of the correct method to enclose the flue..first check these instructions and then decorative finishes will be much easier to decide...if you haven't chosen your heater yet all the instructions should be available on line and this will also help decide the best heater for the space available

The second look like they are designed for stairwells so I'd be a bit wary about using them up higher as the light might be a bit "spotlight" and not diffuse enough. I think both styles work with your house design