Not a nute issue. Its fungal or bacterial. Leaf spot looks a tad greasy and wet-like looking. Which would lean towards more bacterial issue. But, cant be for certain from just a picture. But, your looking at a fungicide or bactericide for that.
Well they can be persistent little fuckers. I have them in my house for a few years now. They put holes all in a cashmere sweater I had. Other than that I haven't seen any other damage around the house. They can be hard to eradicate.
Yeah those are carpet beetles. I worked as an exterminator for 8 years. Hard to get rid of. They wont bother the snake, but they might eat the shed skins perhaps.
System seems a tad overcomplicated for what your doing. I think I see your direction and thought process on it though. Use one way check valves if you want. I prefer an air release valve in some situations. Not an issue outdoors but, might have to position it so its not splashing a bit a water...
Never had them on my MJ, but I grew commercially for years in horticulture. They are not difficult to kill per say, but can get into nooks and small spaces and breed in huge numbers that can make it hard to eradicate at times. Though they are not harmful to plants and they feed off organic...
I can be on the AT from my house in a tad over an hour. Use to love to backpack but my knees suck now. Just have to think about it more than I used to. Can day hike just fine usually but increase the days, mileage, and weight ( gonna have some issues).