I've never heard of anyone saying not to put a filter on your lens---and I do know people who would have had cracked glass had they not had a filter on! It's extra protection. I had a UV filter on my Fuji for three years, never knew it was there, didn't notice a difference in my pictures, but I never had a smear, fingerprint, or a piece of dust on my lens---ever---for the life of the camera!
But if there's a sound engineering/photographic reason not to use one, I'd take that advice! (I haven't bought one for my dSLR yet.)
As for a lens hood, they help cut down on types of lens flare---most of the time I use mine, sometimes I do need to take it off, but it's also extra protection. If you knock your camera and it tips over, it will bounce off your lens hood. (You know those lampshade-looking things dogs and cats wear after surgery? It's kind of like that, on a much smaller scale. So when your cat jumps off the couch and lands on his face wearing one, his "lens hood" bounces off the floor before his face does. It's very entertaining, actually.) The longer the lens, the bigger the hood. The hood for my 18-55 barely noticeable, just a ring around the lens a little wider than the lens itself.