Your questions would be better addressed in the ATG forum.
Ordinarily I wouldn't give a second thought about playing a 4 at 3B. However in the ATG game where everyone can hit and field I have no idea if that is a good idea or not.
Same with question 1. If a guy hits .355 and is a 5R he likely would hit LHP well enough in normal leagues. In ATG it probably wouldn't be good enough without a platoon mate but I don't know for sure since I rarely play ATG.