In the original Star Wars movie, Grand Moff Tarkin destroys a perfectly viable Alderaan seemingly simply to demonstrate imperial ruthlessness. It then stands to reason that the economic loss was negligible to the Imperium, implying immense wealth.
Note there are some that claim that the empire was on the brink of collapse. Presumably, in that case, Emperor Palpatine simply would not have cared. But this is not the sense we get in the first movie. If anything the upper echelons of the empire exuded nothing but confidence!
(Looking at this excellent question we get a possible sense of the way the Empire funded itself.)
Then, can we reasonably estimate the number of worlds in the Empire?
If we can prove a general statement such as 'it comprised the whole far-far-away galaxy' that would be sufficient proof. Also if it leads to speculation we'll remove it