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.

Is your FP wood burning? I have a gas FP in my living room, and I can't sit that close to it, and be comfortable long. I do have a leather chair next to it which is much more comfy for sitting. Here are some images of contemporary fireplace hearths, and you may get inspiration from them. Personally, and this is just for me, I'd prefer something like the bench in front of the FP, so you can more it closer or away depending on the heat emanating. HERE are the pics. My late sweet dog kids liked it for a few minutes on a cold winter day in Maine, but they had to move away soon, too. (Old picture!)

Yes, there doesn't appear to be room for the window trim. I'm looking at the floorboards--where the fireplace framing ends and extending the floorboard line up the wall. When you add backerboard and thin bricks, looks like the trim is going to get buried behind. Photos can be deceiving and it may 'just fit'. But I am afraid that end wall is going to look over-stuffed. Nice view outside; I can understand wanting to hang onto the windows but the problem is having three focal points on that wall and the space issue of too big fireplace or too big windows.