First step: Contact a local mason.

WOW I see some serious issues with thta chimney all that soot cam from somehwere. As for the basement you will need to have it dealt with properly and it is impossiblre to tell from the pics how that is connected to the foundation of the house You might be able to just close it off but that needs to be done right if there is another FP above that one for sure .

@Patricia Colwell Consulting YES! We aren't living in the house - it's a home we are remodeling as a complete gut job before we move in. One of the first things we did was have a chimney company evaluate it. It needs major work to be used safely, so we can either 1) abandon it, 2) use it as a gas fireplace (internal vent which I don't love). Due to needing to place footings for a beam on the floor above right in the middle of the hearth, we want to just abandon it if we can. There is no other fireplace above it. So far the GC's we've contacted have danced around what to do with the fireplace.

To abandon usually involves filling with insulation and permanently sealing up any openings on any floor and the exterior. Be certain of the need for the footing placement, or you may need to remove rather than abandon. To remove a chimney, you start from the top down. Not the bottom up.

We have had gas fireplaces in our last three homes. I like them for ambience, heat. In the last house we had a Heat N Glow double sided and it was outfitted so that embers could light without a fire. It really was lovely on a warm summer night just to have the embers with no heat.

https://www.fireplaces.com/products/8000-series-gas-fireplace

You might want to read this article from Refin as it gives you an idea of what a fireplace adds to the value of your home at resale.

https://www.redfin.com/blog/adding-a-fireplace-can-increase-home-value/

I hope you find some real help the footings are a puzzle for me si Iwould need a lot more info and darwings . The hearth can be removed for sure and honestly as far as the FP goes just seal it up naf move on cover what is left in frywall and treat just like the rest of the wall. I think once yo start toughing that chimney there will be more cost and effect than you might imagine . I think this chimeny maybe served mors than that little FP at one time so make sure nothing else vents out of it. We had the HW tank and the boiler both venting out a chimney thatwe really wanted gone but not at 20K So I designed a storage cube around the chimney where it was in the way , best thing ever,