Good advice Neal.
Interestingly, I think it was St. John of the Cross who stated that all priests should be at the 5th mansion or greater. According to him, no priest is better than a bad priest. In other words, priests who are not holy cause more damage to the Church than if they were never a priest to begin with. He was very serious about this, and I think for good reason. The Church does not need numbers. It needs holy priests. And in this sense, I think you are on the right track, if you have concerns about chastity. Recognizing one’s weaknesses is an important step than many fail to take.
With that said, I do not believe there is a legitimate impediment to entering seminary, unless, perhaps, you are actively viewing pornography. It is expected that a discerning priest have developed enough self-control to resist looking at pornography. However, other lesser forms of impurity may be more of a grey area that one needs to discern individually (the screening process is *supposed *to be able to pick on on this)
Blessings,
-Davide