Should the bottom of the bag be straight?
Not being straight will not hurt the bags. Air bags are run in industrial applications up to 30 degrees. We try to keep the bags straight as possible, but the bottoms may be angled a little as the pinion angle of the axle is set. As far as up and down goes, the kits are designed for the bags to set pretty square. If your application has an adjustable panhard bar, use that to make sure the axle has the same amount sticking out from side to side. Once this is equal, the bags should be straight.