I have a double-level FN and I would suggest getting the double (the 142), it's just cheaper in the long run, if you get the urge to get more babies... :lol:
But yes, if you have girls, or small boys, you'll likely have to wire the whole lot (including the shelf inbetween if you get the double).
Night's cage is amazing isn't it?
Makes me want to get another one just so mine could look kinda like hers. :lol: