Fireplaces, Heating Stoves, Flues and Chimneys - making own mantel, looking for posts on each side

we are pretty handy and have been doing alot of the finishing in our new house.

we really want to make our own fireplace mantel and surround, i found an idea that i like and photoshoped some elements into it. here is what we are going for

http://klearz.com/house/fireplace.jpg

here is what we have so far

http://klearz.com/house/IMG_2122.jpg

the fireplace is already installed at the high of our step. we plan on making the step out of wood, and covering the top with granite, covering the outside with baseboard.

around the fireplace will also be a granite insert, how do we attach that?

then we plan on making the rest out of the surround with wood and trim etc.

#1 question how do we attach the granite

#2 is what we have done so far and planing to do acceptable

#3 where can i find posts like in the picture for each side? what kind of stores should we look at? the few stair stores i talked to didnt have the style we were looking for. as a last resort i found some online but would rather buy local.

You are going to have a fine looking fireplace with the plans you have so far.
The granite should be attached to the backerboard with thinset and grouted with unsanded grout, unless it is in one piece.
The newel post type upright you are seeking should be available in the staircase department of most hardware or big box stores. If you think the ones they have there are too thin, then you may have to buy a full newel post and run it through a table saw to remove just enough of the profile for a flat backing. Of course purchasing online is an option. Good luck with the fireplace!

there is no backboard there, its just a hole!

You'll need to install framing around the firebox and place a layer of cement backerboard on the face to adhere the granite to, setting the depth to accomodate the thickness of the granite.

so is it ok for a 2x4 to touch the fireplace? or do you leave a gap?

looking for an answer to my previous question.

Sorry, I let the post lapse. I must have gone to sleep for a month. Anyway, is the firebox prefab metal, or did you have an existing brick fireplace? If it is prefab, then the insulation factor and spacing to a combustible materials has already been factored in, and you can place wood against the outer walls. There are clips to attach them to as well.
I will keep a closer eye on the post.