New player and some prefered server and End game difference questions

[Naryoril]

3. how do chars/jobs differ from each other in end game, how is one bard different from the other, or is it possible to play a paladin in different way, different gear of skills for ex.

To add to what Raldo already said:
There is a bit of customization of your gear through materia, but the effect isn't large enough to warrant having several sets for different purposes, at least in the vast majority of cases. But even if, since most high level gear i unique and you can have every piece only once, and because there is often no choice of items (e.g. there is currently only 1 set of ilvl 400 gear for each class), it isn't even possible to have multiple sets ready. Yes, you could remove and add materia depending on what you do, but that will be horrendly expensive (because if you don't overmeld this kind of optimization is pointless anyway).

Since every character can be every class, you can look at it as having several "specs". If you want a more defensive "tank spec", play Paladin. If you want more damage from your "tank spec", switch to Warrior. Its one click you can do any time as long as you are not in an instance and not in combat. Apart from the weapon the 2 classes even share the same gear (and you can't avoid sharing the gear, as explained above), so you don't have to collect multiple gear sets.

[Frizze]

and because there is often no choice of items (e.g. there is currently only 1 set of ilvl 400 gear for each class)

I dont disagree with your overall point, but i did want to offer a slight correction. There are 2 sets of i400 gear. The savage set, and the augmented genesis set. Still, even adjusting for preference in sub-stats doesnt really change much(for most classes). Does a ninja in a high crit build play differently then one in a high det build? To my knowledge, not at all. And some classes have stats that are hands down better then the alternative(a bard that isnt maxing crit is a bard that didnt read their tool tips). But as Raldo said, we differentiate ourselves via our class choices(and skill or lack thereof) and via our glamours.