Yep you can reallocate them with an item sold in your GC's seal shop... you won't be able to for a long time, by the looks of it. Don't worry about if you've messed up though. Also to know all classes have their own stat allocation, so you don't need to worry about if you switch to a conjurer, for instance.

If you want. It's not required but you can make some good money if you do gathering and get it to high level. Same with crafting, however if you want to make serious money you need all crafters to level fifty. For a good gathering class I'd recommend miner, those ores are a good source of income for lazy people (like me...I'm like, "I could mine that...........meh" and then just buy it off the marketboard).

I'd do it as soon as you hit thirty on lancer. The class you are thinking is Marauder. There will be class quests again, so just do those. And since it is in a new area (Limsa Lominsa) I would go ahead and save those sidequests in that area for when you're leveling the tank. Also do all FATEs you see, and try out leves if you have them unlocked. I think the first fifteen in any class is so boring...just gotta get through it (because at fifteen you can go into dungeons. I like dungeons.)

You should be getting equipment from a lot of classes but if you find yourself outgrowing it, a good rule of thumb is "every five levels", give or take a level for some stuff. So at level fifteen you can check the marketboard or a shop for higher level equipment. I see it is usually every five levels though.

I see you're on Lich, the Best Server. If you'd like, let me know next time you play and my FC can help you out
I'm going to be playing for a while, so you can /tell me in game if you want. I'll get it unless I'm in a duty.