Good luck with Gunners, Rufus, and Motorball; no save points between any of them although there might be one if you choose not to accept Tifa's help for the fight (not tested it). This advice might be out of date by now if revisions were made, but:
-) Avoid using magic against Hundred Gunner, or queuing more than one spell at a time; his counter hits the entire party quite hard.
-) Avoid attacking Rufus physically, his counter inflicts various status ailments (unless you use Cross Slash to paralyse him but I can't remember if he can be paralysed).
-) Avoid using your strongest attacks on Motorball at the start of the fight; he begins with a Peerless effect that you should wait out until it wears off. The Peerless effect is initially invisible until he is struck, so attack once to make the effect show up. Also, there's a row change on Motorball's deadly wheel which doesn't update visually I don't think; watch out for that as your party members will become more vulnerable to Sword Arm.