Your diet seems ok (in reference to the quality of the foods you eat), though I'd probably add in one more meal in there :P. I would recommend interval training very highly. Here's a brief wiki on it
http://en.wikipedia.org/wiki/Interval_training ... Note the part where it's used very effectively in "cardio build-up". So, if you're looking to build up your stamina I would think interval training would be the way to go. In addition, I've read a slew of articles about interval training's fat burning/muscle sparing effectiveness. As for frequency, I would do them on the days you don't lift weights.
If your weight training regimen is going swimmingly and you're gaining strength then I'd stick with it; the old adage of don't fix it if it ain't broke kind of thing. However, I'd add in some shoulder work in there somewhere; perhaps at the beginning of your leg workout. There are plenty of strength increasing routines all over the board so do a search and see if one of them fits.