Thank you for your inquiry. We do not recommend spraying joint compound. Hope this helps.
It should work fine. That's a bit big for caulk.
ABSOLUTELY YOU CAN! Use plaster weld in areas where you are down to lathe. I'd use the 90 for drying time. You can skim coat smooth walls and over ugly texture with this this. You will do a scratch coat, then another coat. Depending on how bad your walls are you may need a third ooat. You can wet sand them and fill in the the holes. You can also sand the walls with an oscillating tool with the sander attachment. Walls and ceiling smooth!!!! Nice hard cold walls! Yeah!!! They make a finish coat if you want to use that to go over Durabond. I am a 56 years old woman and I did an entire 1923 house with ugly ugly textured walls and ceilings with this stuff. This stuff is great.
It depends on what your repairing and if you will be sealing/painting or covering it up. But generally no would not use this on exterior products. There are many products specifically made for exterior work