賣左樓等樓價跌 is very risky, especially when you have a family with kids.
I have seen many cases like this, all end up regretting their decisions because they have lost so much money on rent later.
But if you don't have kids, it is easier for a couple or a single person to take this risk because their opportunity cost (paying rent) can be a lot less if they rent a very small flat.
DON'T try 賣樓等樓價跌 unless you are very confident in your market judgment and prediction.