I haven't gone that deep, but I've collected a motley assortment of materials for combination. None of them actually combine successfully, mind you, due to inadequate skill level. Can one acquire these skills, or do you need to select them during character creation? Knowing which way it goes would help with inventory management, to be sure. I guess the same question applies to the other skills. I'm tempted to just select all the proficiencies so I'm able to make full use of the dungeon's resources. I suppose I would lose out on other, cooler, abilities, though.
All of the "level 0" recipes are available to all, as long as they have the crafting equipment. In this way you can always smelt ore into ingots, etc. The level requirement is in the recipes menu as the little number with a green checkmark or a red x next to it, underneath the "result" item.
You can find items that give you crafting skills. "Tinkerer's Goggles" for instance, grants 1 tinker (and 1 of each trap skill). You won't have the skill tree perks and such, but you will be able to make better stuff.