While the asymmetrical rims like the A23 are nice from Velocity, I now much prefer their new rim called the Quill. For what it is worth my go to rim was always the A23 from Velocity until recently building a set of Quills for my personal bike and now I am sold. It is lighter and still slightly wider and I really prefer the way a wide rim feels, even with 23's. For spokes, anything double butted and quality should work fine but I personally like to run a slightly lighter gauge spoke on the non drive side of the rear wheel. In theory the lighter gauge spoke is more "elastic" and is less likely to go completely slack than a spoke that is of heavier gauge and less "elastic" since the non drive side of the wheel will be at a lower tension.
For a first set of wheels, brass nipples do turn smoother and are less prone to wind up but you can get away with aluminum if you use a good lube on the spoke threads and also at the rim/nipple interface.
Hubs are more about what fits your budget, I personally like White Industries hub as they build well and last nearly forever. Them being made in the US is also a nice touch. The DT 350 is also very nice and costs a fair bit less than WI, both options have the ability to swap drivers should you ever move the wheels to a bike with Shimano or SRAM.