Well, after breakout, usually the broundry from which breakout has taken place will serve as S/R level. About volumes, if the volume on pullback is very low as compared to volume on breakout, we can assume that the pullback has just shaked a few weak hands or profit-takers and the smart money is still in the trade.
One can take into account S/R and wait for the price to cross but then its a question of individual philosophy and risk taking capability as well. Usually the stocks follow the measuring formula of a pattern but the trend may falter at S/R level. A time stop at those levels along with price-volume level will help the trader in deciding upon his next course of action.
IMHO, breakout was a valid opinion.
Further, about leaving or taking a trade, we are dealing with probabilities over here and perfect setup's are hard to come across in real trading life and we have to take risk in trading but certainly a trader has to take only those trades with which he is comfortable with. There are hardly any Black/White trading methods in markets. All of them has more or less shades of grey which is reflected in the word "probability".
I will also like to see how experts see the things. Waiting for their comments.
Best Regards,
--Ashish