I'm sorry you haven't received any responses to your question. I search Houzz photos for honed limestone fireplaces, and found this one. Perhaps you could email the designer with your question? [houzz=]

Limestone is soft, similar to marble and soapstone. It will stain and smoke will cause it to discolor. Not sure how you would stain it though...unless you are in the habit of throwing wine glasses in the fireplace at celebrations and someone misses! If the fireplace draws well, smoke won't be an issue. Cleaning isn't really an option unless you are going with slab stone, then a sealer and following the advice of the fabricator are your best bet. Take a look at this Indiana limestone mantle:

We have built a few fireplaces with no issues so far using a softer material like limestone. One Travertine slab fireplace and one with travertine tile. The wood burning fireplace did discolour the wall tile a hair but not enough to notice. Here are our two installs with Travertine.





I would suggest getting a sample and applying your sealer a couple of times. Place the tile above your fireplace directly and have a few fires. If any issues arise from the heat they will surely show themselves above the fireplace first.

Often epoxy resins are used with softer stone and this can yellow with added heat.

Good Luck. JW