The anticipation of a MACD crossover (or the anticipation of any other move for that matter) is not recommended. Remember, nothing happens until it happens. As you suggest, it is too risky. Personally, I would rather enter a trade late and be right then enter it early and be wrong.
A good rule for determining a limit on a trade is to simply double the amount of your stop. So if your are placing your stop at 50 pips above your entry in a short position, you can set your limit at 100 pips below your entry. By so doing, you will have a favorable 1:2 Risk Reward Ratio in place.
The link below will provide additional information about trading with at least a 1:2 Risk Reward Ratio...