Welcome,
1) Yes. I have BVC and Subtank coils. They can both be cleaned in the UC. I find the UC more effective at removing previous liquid taste than built up gunk. The cotton in the Subtank coils is as white or almost as white on the 6 coils I have cleaned in the UC as when they were new. I have also simmered, close to boiled, the BVC coils, Have not tried it with the Subtank coils. There seems to be no limit to the number of times the BVC coils can be cleaned, but I get rid of them after the 2nd or 3rd cleaning. I think the cotton in the Subtank coils will begin to disintegrate in time. This may become an issue with the new cotton BVC coils that are becoming available.
2) Propylene Glycol (PG) has antibacterial and antifungal properties. It has been used in the ventilation systems and oxygen lines in hospitals. Vegetable Glycerine (VG) is also antibacterial. Google "Vegetable Glycerine anitbacterial" for more detailed info.
ETA: Some people blow the water out of the BVC coils and use them right away. I let mine air dry for a few days. It is a matter of whatever works best for you.
Happy Vaping!