Hi Louis and welcome to the D50 family!!! I can't speak to the differences between the D50 and the 40s, I can just tell you that after having a D50 for about a year, I haven't had a moment when I've said, "Boy, I wish I had a D40/x instead of this "old" D50. The best advice I've gotten has been that any time that I spend second guessing what I have is time that I'll later on realize I could have been taking pictures.
I started with lenses from my film camera (one new nikon and one ebay 3rd party), bought a new nikon lense, and recently a new 3rd party lense. In the order of how much I use them: 1. $250 Nikon (new); 2. $60 Quantaray (ebay); 3. $95 Nikon (new); and 4. $400 Tokina (new).