Regarding the money, Sheldon does earn a lot more than he spends. He had a drawer full of uncashed paychecks, and actually said a percentage of what he spent each month. Leonard should earn less, given that he seems less academically succesfull and has been at the university a shorter time, but he still should have a lot of money left at the end of the month.
And when we are on the subject, why does Howard work at a university? He seems skilled at what he does, and his field has practical uses, in which there is a lot of money. A private aerospace company should be able to use him much more.