You can max the Shadow Dragon faction before the first major plot point in the game [DAV ACT 1 SPOILERS]

Hopefully the title is vague enough but if you know, you know. That said, to spoil it for those who want to 100% the game in the most minor way possible: you lose access to either the Shadow Dragon or Antivan Crow faction vendor after recruiting Davin. The first quest in that chain is: In Peace, Vigilance. Because different factions require different items to level up, if you want to get every item you need to max Shadow Dragon before the decision point. Antivan Crows cannot be maxed because their last level requires too many of a material that cannot be gathered in the required quantity at that point in the game.

Maxing Shadow Dragon will take a while. The ghost merchant in the Crossroads will sell the Perfect Ore you need. You will spend a lot of time grinding in the pot hallway in Minrathous and make sure you do the sidequests that open up there before recruiting Davin. If you are super-efficient you could probably do it in 3+ hours and it takes that long because you need to buy all the crap too. You can do other stuff while you grind, it is very mindless.