I read on here somewhere that -ski last names were originally used to designate royalty or elite families. Correct?
That is correct.
-ski last names were the names of noblemen. In the times of the First Republic
szlachta (noblemen) constituted 10% of Polish population. That's why those
names were very desired by, for example, newly rich peasants who very often
changed their names to noble ones (i.e. Kaczmarek -> Kaczmarski).
Many Polish Jews also changed their names to Polish sounding ones and they very
often chose -ski names.
-icz names were also noble names but they were associated with eastern part
In a present day Poland -ski names are very popular, but they are no longer
associated with nobility.