14/15 spokes and brass nips will suit you just fine.
we use wheelsmith spokes at my shop, and i've never had a problem with them. i'm actually in the middle of building up a new set of race wheels (road) with wheelsmith spokes, light & aero.
the double butted spokes are more durable for a couple of reasons.. 1) the 15ga part in the middle is a little more springy, it'll handle shock & vibrations a little better, 2) all that shock and stress is directed to the 14ga parts at the ends of the spoke where the spoke can handle the stress a little bit better.
brass nipples, well, i'm a bit timid when it comes to aluminum nips. i've replaced one too many cracked/rounded al nipples to want to put them on my own bike. someone of your weight (no offense) is going to be putting more stress on a wheel than a flyweight, so the extra durability will come in handy.