One Character for Everything or Multiple Characters?

[Enkidoh]

Welcome to Eorzea!

1. You can reset your spent attribute points later in the game after you join a Grand Company (which is part of the storyline) - its a consumable item called 'The Keeper's Hymn' which you buy with company seals from it's headquarters. Also each class has it's own set of attribute points you spend on one class will not affect another.
2. Stat differences between races and racial clans is pretty much trivial at the start and virtually non-existent by the 'end' of the game, so it comes down to appearance really (you could go as a lalafell PLD and still tank just as well as a roegadyn for instance). Plus with the aesthetician and the Fantasia items which allow you to change your hairstyle/hair colour and race/clan/gender/physical appearence respectively, even that is not 'set in stone'. And with the Armoury System that allows you to change to any class you wish whenever you wish, there is little need to create alts if you're just unsure about what to play as. So feel free to experiment!

As for effectiveness at end game, all classes and Jobs have their uses and weaknesses - find one that suits your play style (PGL upgrades to MNK later in the game and is a pure physical dps incidentally).