Händlmaier is hands-down the best Weißwurstsenf.

Most recipes I have seen call for a small amount of lemon zest. That provides the flavour without adding too much acidity or bitterness.

Looking at that, I'm sure this would would work very well with Kangaroo instead of the venison. On my "must try" list now

Looking good! Kangaroo meat is super lean, and it turns into shoe leather before you can say "Kangaroo" :-) When cooked as a steak, the best way to eat it is very rare, bordering on blue. For sausages, 30% pork back fat or so will do wonders. As you say, the flavour is quite mild, not anywhere near ...

All looks excellent, well done!

No real need to disinfect as such. Just clean really thoroughly with hot soapy water. If you are really worried, you could use an iodine-based disinfectant, such as the one used in cheese making. But I don't think it's needed. Just work cleanly, and you'll be fine. Be wary of vinegar, lemon juice, o...

I strongly suspect that eating those casings won't do any harm. It's just that it might not look all that great…

It'll definitely be safe. Check the flavour once you have reached your target weight. If you find it too sour, either reduce fermentation time/temperature next time, or reduce the amount of starter culture.

Chances are that it'll come out delicious, regardless

You are controlling humidity to better than ±5%. That's probably about as good as is reasonably possible.

I don't have first-hand experience with a such a set-up. But keeping humidity within a 10% band seems OK to me.

I don't see the need for venting if you have both a humidifier and a dehumidifier. All it would do is make their job harder. I would just try it out without a vent for a few months and see how you go. If you find that you run into problems, you can still cut a vent later. And opening the door for a ...