No it doesn't matter what you pick for those. You don't get much except for a strength sphere. If I remember correctly there was also a scene where Wakka gives the Aurochs the trophy they won during the tournament. An easy way to beat the Goers is complete the Jecht Shot Mini game on the boat that is going to Luca and survive the first half. After that, equip Tidus with the Jecht Shot and try to get close to the goal even if there are two defenders, don't bother trying to break to them for the Jecht Shot will take care of them. Hope this helps.
Edit: Yeah you can beat the chocobo eater in the Mihen Highroad. Start by casting haste on Lulu because the Eater is vulnerable to fire. Blind the Eater with dark attack and use power break. You need piercing weapons to inflict normal damage on it. If you inflict more that 500 damage the chocobo eater will fall on its back. It will lose it's armored status so if you can try using an aeon's overdrive. Rinse. Lather. Repeat and you should be able to beat it. But no you don't have to beat it you just get a free chocobo ride which is useful in getting items in the old road.