questions and more questions

[Enkidoh]

Welcome!

1. Only if you want to do the optional Ixal beastmen daily quests at level 50. But otherwise levelling crafting and gathering classes is entirely up to you.
2. No, each Job has a specific secondary class it requires to be at level 15 before you can unlock it. You just can't choose any class to level for it sadly.
3. Materia is a means of customizing gear by infusing it with extra stats or elemental properties. Not all gear can be infused with materia though - only equipment that has circular 'slots' in it can be infused. Materia is gained by spiritbonding gear to 100% and then converting it, the ability to both convert gear into materia and infuse gear with materia is gained by completing two specific quests at level 19 from the Goblin NPC Mutamix found in Central Thanalan (in a camp far to the north of Black Brush Station). Although once you unlock the ability to convert materia you do not require a crafting class to actually convert spiritbound gear to materia (as it's a 'default' ability you can equip on your Hotbar regardless of class or Job), you do need a crafting class at a specific level to infuse materia into gear, as well as a special consumable item that can be bought from the Market Board that acts as a catalyst to do so. The in-game tutorials that appear when you unlock the abilities will guide you through the basics of the system.
4. Nothing is really known at this stage, other than apparently they have no base class. How that will work is anyone's guess though. But SE will reveal more info prior to the expansion's launch.