So just to be sure...that overheating is normal supplying only 140mA?
Probably not, but depending where you got the 7805, probably China right?, I would not be surprise that it does. Any way those unit, if I'm right, are flushing all the unused juice to the ground so it's pretty normal that it get kinda hot, but how hot is it? Have you tried another 7805, maybe it has a little defect. But what really matter after all, if it's not hooked on a battery, is it sending a steady 5volt at the output?
Tel me, have you tried to put OPENWRT on it? Do you plan to? And if you do, please tel me about your experience.