Welcome aboard! It hasn't been that long ago when I got started fly fishing, and I can tell you from experience, without this site, i'd never have made it. As to answer your questions, I think most everyone will say a 5wt is a good place to start, if you are only fishing streams, ponds and such. I don't know anything about fishing the saltwater, though I'd love to try sometime. Best advice though, is just get out on the water and go fishing. And practice casting alot. Although, I think you'll be better off if you practice about 20 to 30 minutes at a time. that way you don't get tired and start bad habits. Don't be bashful asking your questions, there is a ton of information available here on this site as well as the web, but sometimes that is overwhelming, so don't be bashful.
good luck and again, welcome aboard,
hNt
"If we lie to the government, it's called a felony, when they lie to us, it's called politics." Bill Murray