Actually, you can get maxed stats in everything except Luck, MP, and HP with the nodes that are provided, including unused nodes. You just need Purple Spheres (Species Creations drops) to place +4s where necessary.

To beat Don Tonberry without resorting to level-ups, simply start the battle with characters that haven't killed anything (Yuna, Rikku, maybe Kimahri) and attack as often as possible. He will only Karma you for low damage, the calculation being roughly (kills * 3). Just attack as normal, until he gets closer to you.

Everytime he takes a turn, he takes a step, and once he has three turns, he will remain in the Chef's Knife position, which means your only concern is his Knife, which can attack multiple characters. Cast Protect (assuming it doesn't kill you in one shot), Hastega, and bringing more powerful characters, if you can break 9999 damage. Since you have Celestials, I will say that you can. He stops using Karma as a counter-attack, after that point (I've yet to see him use Karma, if he does).

Don't use Trio of 9999, you are just shooting yourself in the foot, and those little blood cells will come back to haunt you in your sleep and bleed you until you die from heart failure or shock.