In logistics pipes, there was a supplier mode Bulk50 that would supply an inventory with a requested amount of items, but would only request/craft more of an item once the supply dropped below 50%. This was useful as it batched together crafting requests. Is there an equivalent way to get this behavior in AE2?

As @mindforger said, there is no threshold/stockkeeping behaviour for any external inventory at all. Interfaces might fit to some degree, but it is only a batch of the missing items, so it might be just 1.
A more fine grained solution is basically up to the user to build by combining various parts like level emitters together.

I don't think you can have this treshold behaviour but you can configure an interface to provide a defined number of items and add a crafting card