On Poison and Disease
I personally have a strong issue with the posion rules as they stand. Right now, only a few poisons are truley nasty, and most have either very low resistance TN (usually a 20) and a slightly higher treatment TN (usually a 30). The problem is most PCs have an earth of 2 or 3, and aVoid pretty much assures a resistance. If the PC has a medicine of around a 3, they can usually treat anything. Yeah, a high poison craft skill can let you make harder to resist poisons, but they don't really increase in effectiveness. What Poison needs, is both more lethality AND an abilitytied to poison crafting (say calling raises) that increases the effects. Say, maybe 3 raises allows you to have the poison kill. 1 Raise maybe increaes the duration one "unit" another raise or so adds damage (or enhances status effect) something like that, I'm not keen on how may raises equals what effect (I leave that for debate), but just some thoughts to start off.

I find that 3 Earth and a Void point hardly comes close to assuring resistence. It gives you slightly more than 50% chances. Since Earth 4 is pretty rare among low-mid Insight Rank PC's, high damage poisons requiring TN 25 to resist are tantamount to flat-out killing characters. I do agree that treatment with Medicine should be slightly more difficult, though.

Well, 3k3 nets you an average of 18ish on an exploding die. Adding a Void will typically set you at around a 24. Most of the diseases and poisons have a TN of around 20-25, so you're not too bad off, a tad in trouble for the higher TN sicknesses, but not terribly much. One advantage (Jurojin's Blessing) and you are pretty much immune to disease and poison, unless a master is poisoning you. And unless the poison NEVER ends, you'll either eventually make your resistance roll, or the poison ends. They just don't do enough damage to really kill you. Well, unless they are delievered by a Katana...

You might want to look at the poison metsubishi rules (pg 163) for inspiration. As far as I'm aware, it's the only place that proposes the introduction of additional poison effects in exchange for raises.