Yeah, i guess it's a bit of a risk buying the unknown.
Anyway, for my next race wheel build i'll most likely be going with Carbon rims from
http://www.m5-ligfietsen.nl/site/EN The price is right for them. Their hubs are nice as well, and supposed to be very good, and they're light, but i'm not sure what i'll be using. I have to decide on the frame i'm getting first, it's a tough call between the Alloy and Carbon Canyon, though i'm leaning towards the Carbon (enables more parts choice) and the i have to decide how i'm going to keep my bike legal, which might invole the Hub choice.
To answer the other questions. Tubular? yes for dry opens only, (alloy rims in rain, and strong wind). Dura Ace hubs? It's one of my choices, i'm thinking either Dura-Ace, M5, or White Industries, and i'll probably go 24 spokes front and rear. DT spokes? I'm thinking Sapim Cx-rays at the moment, though DT Aerolites are simmilar, so it'll come down to cost, but if i wanted the lightest, it'd be Pillar Titanium spokes.
For climbing, you generally want light weight rims, which also help acceleration, though you need the depth for the aero advantage when the road isn't going uphill (have to reduce the resistance against momentum as much as possible). For a flat race heavier rims are usually better, that's why the Cosmic Carbones were always said to be good for flat races, since the increased rim weight maintained momentum, though i think the newest version of them are lighter.
I'l try and calculate a rough cost for the wheels i'm thinking of building, but if you're thinking of something more similar to Ksyriums, or want clinchers, i'd probably go for some 30mm niobium rims, built to whichever hubs you want, 24 spokes front 28 rear.
I'll leave you to ponder....