1. I'm not 100% sure because I don't game fatigue or play at Petco often, but without AAA I'd say 1300 and with AAA I'd say 1150-1200. It depends on the quality of the AAA.
2. It makes a strong impact because not only do you throw out runners because of the good arm, baserunners in general make less attempts. I don't have percentages, although I know that it was discussed in a forum a while back (Search for Johnny Roseboro)
3. I have no answer on Bresnahan's performace other than it is small sample size and to tell you to look at his actual fielding percentages (not just the letters) as this is a stronger indicator of performance than a letter grade. Also, if you are using poor fielders and deadball era pitchers, then the likelihood of errors will increase as fielding normalization from the era of the pitcher downwardly affects error rate.