G'day. Spent a few weeks familiarizing myself with modding this game. Loving it. 

Can I - and if so, how can I - mod which Wearables are considered "INF" (infinite) from game start?

I want to make a grindier mod where different Outfits, Weapons, and Extras are available from start, and they the player works up to the standard stuff, then onwards to higher level stuff. I've already made a tonne of custom wearables, but cant seem to find anything unique about the wearables in the 0Starter list within Wearables that distinguishes them from other items, other than the "loot" field = none.

The starting items are, as far as I can tell, based on the default gear of your currently available classes.

The least janky way to give the player guaranteed items at the start would probably be to mess with the tutorial encounters, adding a hidden enemy that applies a hidden token that adds your items to the inventory at the start of the next day. 

I'm modding in exactly this at the moment. The next game update should allow you to specify which items are infinite in the guild by default, and also set your own number for how many copies are needed for the item to be infinite ( the default is 4, or 2 if a specific destiny option is chosen at game start).