*In the interest of disclosure, I work for a bike shop (www.bowcycle.com
) as a mechanic.*
We don't sell many 29ers, mostly as a product of the twisty, technical singletrack around here that really benefits the nimbleness of a 26". From what I understand, they are quite nice for faster, less technical riding though. My 26" experience can be transferred to the componentry, and I think you're mostly on the right track.
For brakes, I'd look into the Juicy 7 if it's cost is an option. The external knob is not simply a reach adjust, but a pad contact point adjustment. It basically forces more fluid into the system to adjust for discrepancies in bleed quality or pad wear. It's really handy if you're anal about having your brake levers pull similarly left and right. Speaking as a mechanic, it's really, really handy. It can be quite difficult to make each lever pull the same just through bleeding, especially with long brake hoses, so that little dial is a godsend. According to Avid, the weight is 2g less for the Seven than the Five.
Other options for brakes would be the Magura Marta or Marta SL, which are a great product that we've had few problems with. I'd shy away from Hayes (or HB Performance Systems, since someone else bought the Hayes name), 'cause their formally great product has gone downhill since they started doing greater volume. The new XT is a fantastic brake as well.
I really don't like Rock Shox forks. They've had many, many problems with leaking and blown cartridges out of the box. The Reba, being a high end race fork, may not have as many problems but I'm still a bit soured on the company's recent offerings. I'd go Fox, but as you mention the OE fork doesn't have high speed compression. If you're building a bike from scratch, you'd be getting the RLC version, of course. I really like Fox forks, the only real maintenance problems I've seen are from people leaving stanchions dirty and wearing the anodized coating off. As far as I know, Marzocchi doesn't make a 29er option.
For hubs, I'd go XT. Widely used, which means that replacement parts are widely available. The last thing I'd want would be to be in the middle of an endurance race, have my freehub go, and not have the replacement part available for 7-10 business days. May not be as bling as Hope, King, Mavic or other boutique brands, but are a proven model. Still use loose-ball, angular contact bearings, which means that almost any bike shop, or even auto parts store will have your bearings. They may have slightly more maintenance than cartridge bearings, but are way easier to overhaul and like I said, parts are widely available. The XT wheelset is also really nice, but I'm a 32-spoke, 3-cross, 2.0 mm, handbuilt wheels kinda guy.
You're on the right track with your dream bike, I'd say.
Are you looking for a flat bar or riser? Carbon or alloy?
Stem, I'd go thomson, just to match the seatpost.
Tires: tubeless or tubed? For a good all-around dry + a bit loose tire, I'd check out the Maxxis Crossmark in a 2.1. I'm running these this season and they're great in the hardpack and okay in some loose stuff, but they're not a mud tire by any stretch. They load really fast. Panaracer Fire XC Pro is also a good, albeit tubed, option if you're on a budget. Some people hate these, but I've had good luck.
*Also, in the interest of disclosure, I did get a free T-shirt and some socks from Shimano last week.* :P