Offset and deflection should be checked with a new belt for best results. Take it out and drive it, warm up the belt, then pull it into the garage. You're looking for there to be about 1" - 1.5" of "play" in the belt at the middle between the primary and secondary. The upper edge of the belt should be sitting just slightly out of the secondary (think: the thickness of a dime).
For the chain, that's simple... Loosen the jamb nut on the tensioner and screw the bolt all the way in by hand. Give it a good, solid twist to make it as tight as you can using only your hand. You're not looking to really torque it here, just get it tight. Then, back the tensioner off 1/4 turn, hold it in place, and tighten the jamb nut.