Those IRD rims are not only extremily good rims but you would have to pay at least $1,000 more to get anything even slightly better!
I don't know much about the Velocity hubs, they are a lower end hub but people seem to like them, if you have a tight budget stay with the Velocity.
The spokes you chose are great, but if you want more of a aerodynamic wheel you should consider oval spokes over the DT Competition's. Look on that web site I think they give you choice of oval spokes just chose the cheapest because they all work within 1.5% of the Sapim spokes aero wise which Sapim admits on their web site.
It's good you chose brass nipples because they will last longer then aluminum.
I'm the type of person who prefers to overbuild, so this next piece of advice is based on that mind set. The number of spokes per rim you selected to me is a bit low for your weight. If you want a dependable long lasting rim you should consider at least 32 or 36 on the rear (can't remember the drilling options for IRD), but go with the highest then go with the next one down for the front. And because of your weight and climbing mountains which puts a huge amount of stress on wheels you should seriously consider 36 on the rear and 32 on the front, unless they don't offer a 36 then 32 on the rear and 28 on the front. You will get people that will tell you it's ok to build with less spokes, I disagree, but in the end it's an opinion, and a decision you have to make.
Also I would go with 3 cross on the front because 3 cross is a bit stronger the 2 cross and you'll be using less spokes on the front so you should have the stronger lacing, and it won't effect the weight of the rim by more then 1 gram! So go the strongest way.