Trying to understand this goal… am I supposed to own buildings that rent out a total of 20 apartments or am I supposed to actually rent 20 apartments myself . All the other goals (including own 1 building) use the word own and this one says rent, so I’m thinking it’s the latter (rent 20 apartments myself). If the latter, what’s the point?
Yes - renting multiple apartments - just in case you need more than one option of where to sleep for the night! 
I’m not sure the map is big enough to require anyone to rent 20 apartments.
Remember the conversation we started where you suggested I play The Sims more, because that’s what they want is for us to spend the money we earn from our successful businesses on something.
Why earn so much money if we can’t use it for anything other than investing in more companies?