WOW! So much feedback and so many questions. Thank you! I'm really excited to get this much input on the class. You really helped with the magus of blades and I'm hoping to bring this class up to that same standard.
I hadn't really made up my mind on poisons. My thought is that since the poison disappears after 1 round and can't be created as an attack, you can't use ingested or inhaled poisons and most injury or contact poisons are severely nerfed. Plus, if you've never encountered it you can't manifest it. Alternately, you could conclude that except for the basic poison listed in the PHB, poison is not a mundane object and can't be manifested. I suppose I could explicitly restrict to "items on the PHB equipment tables, and other items with DM permission."
Hmm, I had a thought. I think what I'm hearing from you is that the power of magic items scales much faster than the power of class features. Have I got that right? In that case, my features that add both more magic items and increase the maximum rarity for all items is excessive. Going from one uncommon item at 3rd level to two rare items at 8th level is a big deal. Getting three very rare items at 13th level is an even bigger deal. What if 3rd level gives you one item that is uncommon, 8th gives you one rare, 13th gives you one very rare, and 17th gives you one legendary? This greatly reduces the snowball effect of more and more powerful magic items.