You would have to define what you meant by a 'standard' bus. There are small buses, there are commuter buses, there are school buses, there are tour buses, there are coach buses. For a small bus of...
Probably about 3 tons, considering a normal executive car weighs about 2 tons, and a limo is obviously bigger and normally has more luxuries inside
Between 13 tonnes to 15 tonnes
Classified info more then 5 tons I'd guess.
Varies by frame length, number of seats, etc. Typically, anywhere from 22,000 - 33,000 lbs. GVWR - that's fully loaded.