A separate self is merely conventional reality, in the same sense as lines of latitude and longitude and the measurements of the clock; which is why one of the means of maya, illusion, is measurement.
Things are measurements; they are units of thought, like inches are measurements. There are no things in physical nature.
How many things is a thing? However many you want. A “thing” is a “think”, a unit of thought; it is as much reality as you can catch hold of in one idea.