In mathematics nothing IS a single thing!
It is certainly possible, and done in some treatices, to DEFINE "0" to be the empty set, then define "1" to be the set whose only member is the empty set, define "2" to be the set whose only members are "0" and "1", etc. That means the "2" is a set containing 2 members and, indeed, "23" would be a set containing "23" members- but not just any such set.
I don't know what you mean by "And if zero is the empty set, would be 3 emtpy sets equal to 1 empty set." 3 sets of anything are not "equal to" (in the strict sense of "are exactly the same thing") a single set of anything- three sets are not the same as one set. Since you are talking about sets, you might mean the union of the sets: in that case, yes, the union of 3 empty sets is indeed the empty set.
Or, since you are talking about numbers, you might mean the sum of the numbers "represented" by three empty sets. In that case you would have to define such a sum. That also can be done and, with the usual definition, yes, again, the sum of "three empty sets", that is 0+ 0+ 0, is, indeed, 0 or the empty set.