Was going to participate in Crafter debate, then realized it was likely to cause a derail.
As for the power:
Definitely don't make it -0. If it were -0, then why wouldn't everyone take it?
And don't give a non-mechanical answer. Balancing crunch with fluff leads to people having to choose between playing what they want to play and getting the most out of their character, which is bad.
I'd say that 2 refresh would be enough for:
4 slots.
Ability to use Contacts and Resources to get items.
Ability to maintain items.
Ability to get extra uses of EIs with mental stress.
Ability to Declare potions on the fly, with story of how you got them.
Ability to buy Refinement for more slots.
Starting with a selection of weak items.
Basically, it's Ritual (Crafting) with Contacts/Resources rolls instead of actual Crafting.
Chop off some of that if you only want it to cost 1 refresh.
Bear in mind that owing to this game's basic structure this power will always have balance problems.