Once I get comfortable with using my D 5000 in manual, I will probably want to upgrade my camera. I'm still debating the Canon vs Nikon issue but I see other users prefer different brands. What would you consider a GOOD DSLR? Also, I'm thinking I should switch from DX to FX. Someone said my DX lenses should fit a FX camera body. Aren't Sigma lenses superior?
So many questions here. :-)
1. Canon vs Nikon vs Sony vs Olympus vs Panasonic vs Fuji vs Pentax doesn't matter too much, but especially with the first two. First decide what level
camera you want (full frame/crop sensor, pro/prosumer/consumer). Then you can worry about the brand.
2. The D5000 is a good DSLR. The Canon 1DX is a good DSLR. Ok, the 1DX is a great DSLR. They all take really good pictures, the difference is some advantages in getting more "keepers".
3. Yes, Nikon DX lenses will fit on an FX body, but I think
it should only be done for some very good DX lenses. If you are upgrading to a $2k camera, get some lenses to match. Canon EF-S (crop) lenses will not fit on a Canon EF (full frame) body.
4. Some recent Sigma lenses are excellent, especially in the Art-series: 18-35mm f/1.8 DC (=DX), 35mm f/1.4, 50mm f/1.4, and 24-105mm f/4. Except for the first one, which is unique, there are comparable lenses from Canon and Nikon, so you get to pick the one you like best.
Keep asking questions, it's a good thing. It means your mind is working away, and you're clearly not lazy. ;-)