Solved Thin walls crack apart

How thin are we talking?
What size nozzle?

You can CAD walls (or any detail really) that are too thin for a given nozzle, some slicers do a better job than others, but mechanically speaking you can do it

If you really need a resolution that exceeds what the nozzle is good at I'd suggest a smaller diameter nozzle (which will mean slowing down the print speed as well).

 

Sure, it does.
Again this is slicer dependent.
Some will not try to do infill below the "impossible" threshold and convert those to solid walls.
You probably need to start experimenting with other slicers or at least dig through all the options on the one you are using.

Here the FAQ entry from Simplify3D (not precisely your issue or slicer, but interesting to read):

I’m having problems slicing models with very thin exterior walls and details
The first place to investigate is to compare your extrusion width setting to the size of your model. In order for the software to slice your model, your extrusion width setting needs to be smaller than the model dimension. For example, if the wall of your model is .35mm thick and you have the extrusion width set at .40mm, the extrusion is actually larger than your model. This will cause slicing problems because the software is attempting to place the line of filament "inside" the dimension of your model. When the extrusion width is too large, the filament will be forced "outside" the model dimension. Therefore, the model will not slice properly and your model will will have holes in the Previewer. To resolve this, there are two methods- you can decrease the extrusion width or make your model larger. If you cannot change the size of the model, try reducing the extrusion width. For example, on the .35mm thick model described above, reduce the extrusion width from .4mm to .3mm and the model will slice perfectly. Note, the extruder head will have trouble printing an extrusion width smaller than the nozzle diameter so try to keep the extrusion width setting within a close range of your extruder nozzle diameter for optimal print quality.

 

You can also just adjust the "Outer/Perimeter Shells" which will add more of them and less infill.

 

Yes. under extrusion would affect the entire model, but smaller/thinner parts would be worse off

 

Moisture (I like to cal it wet filament) will normally only cause visual imperfections, but the smaller the part I would imagine the more likely it is that these would become structural imperfections. I have never managed to have wet filament cause any structural issues (your mileage may vary).

 

All wet filament with the exception of rolls still sealed (darn few)