Actually, I think the term you wanted to used was 'raised firebox' but I think we all understood your question. ;-) By 'no mantle' and 'no surround' do you mean that the firebox will be installed flush into the wall with painted sheetrock coming right up to the edge of the firebox on all sides? Like this image ... I think maybe a simple concrete bench made that fits flush with the bottom of the raised firebox and is the same width as the box or 36 to 24 inches wider than the box would look nice. Maybe in a style like one of these: Concrete can be faux finished to coordinate with other finished like marble, granite, etc. And, if you ever decide that you no longer want the bench in front of the fireplace, a concrete bench, even one with a faux finish, can find a new home in your garden.

Cultured stone and other natural stone tiles (travertine, marble, granite, etc.) are typically applied using a fortified thinset mortar which bonds very well to unpainted brick. So it's pretty easy to install it over your existing brick. There's nothing wrong with installing a picture hook using a screw into the mortar so long as they used the right anchor. It's easy to install it into any new surface also by drilling and using an anchor.

We have both. We did a raised hearth in our living room. A wood burning fireplace, not gas. Did the raised for a few reasons. Although the fireplace opening is fairly large, I wanted it raised for sight lines. I wanted it raised for the same reason Weedy wrote, that it actually does provide additional seating when needed. The raised hearth also makes access easier for me when tending the wood fire. My kids were young, 3 and 5 years old, when we built this house. Though the hearth could be considered to be a hazard of some sort, it also acts as a "stopper" or sorts, keeping the kids from running around right in front of the fireplace opening. My kids loved the raised hearth; sitting and watching the fires, warming themselves, etc. In wintertime it was one of their favorite spots for sitting and reading. There are differences between gas and wood fires, so your priorities may vary. Upstairs in our master bedroom suite I have the firebox raised off the floor, maybe 12" or so...but instead of raising the hearth too, I built the hearth itself flush with the floor. Up there I didn't want a raised hearth at shin level when someone was moving around in the darkness. We wouldn't ever use a raised hearth up there for sitting, we have a couple of reading chairs set around the fireplace. Though the room is generously sized, I didn't want the raised hearth projecting into the room. Raising the fireplace box itself still gives nice sight lines of the fire from throughout the bedroom area, even when in the shower or tub in the master bath, and the "flush with the floor hearth" preserves some square footage. So for us it was two different rooms, two different sets of priorities. And do realize your kids will be young and reckless for how long? Whereas the hearth will be raised or flush forever.

I like both, but I think a floor level fireplace in your living room, would be a little more formal, while a raised fireplace in your family room/kitchen area would be more informal. I know you want to use the stone in the kitchen. What do you plan to use in the living room? Are you going with something more classic/traditional, like Monablair's second fireplace? IMHO, this would give each room a different feel and a little different purpose. I know you have a TV in the kitchen now, so a more informal, kick back and watch TV or help with dinner would be a nice balance, to a more formal, sit down and relax, have a nice conversation or maybe watch a little TV in the living room. Also, a nice white classic mantle (with maybe a marble surround?) would be so perfect, with your beautiful butler's pantry. More classic/formal in the front rooms, and more informal, casual cottage, in the back :)