That is a tricky question on the glass. What are you going to be doing most of the time? What is your budget like? With out any background info it is hard to determine what lens would best fit you. The only lens that I can suggest with out any info is the nikon 50mm f1.8 prime lens, that is a must for anyone. It inexspensive and it have great optics and is fast.
i can't be positive but i'm pretty sure he meant to say off.did you mean once that flash is ON camera?
I dont think the D50 can do wireless if I remember right. I havent used one in so long though that Im unsure.