You can do it either way. You could install the wood first and all the marble after. Or you can do the whole thing and put the wood over the marble. The second method will be more expensive snce you will need more marble. On the other hand, the installation of the marble will be easier since you won't have to cut around the wood. Either way you can install the wood surround and mantel using the correct construction adhesive (see label on product) or attach it with screws (or even use both). My preference is to use at least some screws. If you use screws, get some lead anchors and drill into the brick/marble with a masonry bit sized to match the lead anchors. The screws then go into the lead anchors and will hold fast. Also, make sure that the clearance from the wood to the fireplace opening meets the minimums prescribed by your local building code!

I use a photo editing program (MS Digital Imaging Suite, which is discontinued :( I capture images from the net with ScreenPrint Platinum and then cut and paste materials into the photo. It's pretty much cut & paste, although I have taken to a lot of the other tools to work with color and blending, etc. Someone recently posted a free photo editing program ... You can either superimpose (paste) or also cut the stone out of your original picture and place the new material behind in the blank space, which might be an easy way for you to go. Usually the net images are too bright, so tone down the color a bit using the saturation and lightness/darkness features in the coloring tools. Feathering the edges with the blur tool is another good tip. I would say it seems you have enough detail with the grill and mantel, so it's hard to imagine putting pebbles in, which does seem off in style as well with the mantel. Not that we need any rules :) I do think they look very pretty together with a simple, plain surround, though. I only tried the soapstone, low contrast, which I find keeps it very simple to let the details of the mantel and grill shine. Everything shouldn't be calling for attention or it will get too busy and confusing to look at. I'm sure you know what I mean :) Such beautiful pieces!

One of the things that gets me all twisted around in these types of choices is the historical context. The most appropriate choice from a decorative standpoint may not be the most appropriate choice from a historical standpoint. The most appropriate one may not be the one that looks better. But if you are changing it out of necessity, maybe letting the historical trump the decorative is kind of revisionist anyway because it's not really historical, it's a replacement. See how I can twist it around? But part of the issue is that in the US there is such little historical fabric. I was talking to a patient from England who said that the house she grew up in was 500 years old But as far as the interiors went, they did not necessarily pick a bathroom tile or fixture based on needing to look "appropriate" in a 500 year old house, because what IS such a thing? Here, we try to preserve each element because of its rarity, but when it comes to having to Replace, what then? Maybe if you are replacing it with something that was not there to begin with (I doubt there was a marble facing on the firebox on the second floor of a house like this) --maybe you can replace it with whatever you like. (?)

OK, it's not granite. This is very different from what we imagined (It's not a polished granite). I'd continue the cleaning (very diluted version of muriatic acid) until you have the mortar joints as consistent as possible. Then do the "wet test" to get a visual: wipe/dab with a wet sponge and see if you like it. This will be the more extreme "seal and enhance" effect. Let it dry for days and then use a stone seal and enhance product. Talk to the suppliers in your area about a seal & enhance product that is used in stages. Start light and reapply to your desired sheen and color - use a dabbing technique. Always start in the most inconspicuous area. That's what we would do. You need a little more elbow grease first to clean up the mortar. . Good luck.