-You unlock it after the second(first, really) mission, along with Mog Locker.
-The 'level cap' per say is the highest level in the party. Monsters are based around that level.
-You have time limit to find the end.
-You can only Assault at places that you supplied(think Outpost). You do your first supply quest on the second mission. You also can teleport there at cost of (whatever-signet thing) points.
-You can buy a lot of different kinds of armor with Assault Points(which you get from Assault). This list includes Yagit set(the mage one with MAB). I didn't check the whole list, but I can add it on. There are 7 NPCs (atm) for these region/outposts/Asssault. Each one has their own store for your points and mission lists.
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