Well, Kira and Tocsin covered most of what I would have said, but I can offer a couple additional thoughts.

3) Tanks usually get nearly instant Queue times and Healers not much longer. DPS is the longest, but rarely by enough to cause real problems. During peak hours, DPS will typically get in in about 15 to 20 minutes (and there's usually plenty of other things to fill that time with). If you play off-peak hours, though, it may be longer.

If you plan on playing multiple classes anyway, one thing you might consider is using dungeons to level your tank and healer classes while saving quests for your DPS classes. This would include using a DPS class to run though the majority of the main scenario, making it your first "main" class (though you'd want to keep a tank and/or healer near the same level and it may take over as "main" at endgame, depending on to what extent you choose to treat one job as your main one).

4) Go with whichever you enjoy. Personally, I like Bard because while it's primarily DPS, it also includes a bit of support as well, watching your healer's mana levels and singing a song to increase MP regen when needed (or other songs to increase TP regen or casters' magic damage). That and the fact that we can move while attacking make it a fun job to play. Its only downside is that it lacks a good Limit Break.