I think better will be to check this info on their website. As I know there are special recipes for burgers which are available for vegetarians. You can order such meal in restaurant, cafe or prepare it by yourself. I also recommend to pay attention on different cuisines, there are so many cool dishes! For example my favorite is portuguese foods, you can order such products even online!
Good question. BK's website has no info on them. I get them by the 6-pack. They are so good. Put White Castle to shame. I'm betting 120 calories per slider/no cheese. A Mcd's QP w/ cheese has 510 calories. W/ no cheese (2 slices) I guesstimate 370 calories. The slider being roughly 1/3 of a QP, I come up w/ 120ish calories per BK slider.