I agree that it's not practical to disassemble a coupled tandem simply for daily storage. As far storing in an apartment, I think the stairs/elevator are more an issue. Is the basement really not viable? Can it be locked/secured?
Regarding riding single-these bikes handle completely differently with a stoker on the back, so you really need to practice with both of you on it.
Regarding waiting-last year at this time my girlfriend wanted to wait until next season to buy ours. I am so glad we did not wait as we would have missed out on thousands of wonderful fall and even winter miles.