A: The package says not dimmable and not for enclosed fixtures. I'll attach a picture. I don't know if a dimmer will damage them / shorten the life, of if they just wont work.
A: Generally only if they are officially designated 'Enclosed Rated' should be used. The electronics that lowers / regulates the voltage to the LEDs need to dissipate ~ 10 Watts of heat. This heat builds up in the enclosure and overheats the electronics. It may flicker, lose efficiency, shut down or become permanently damaged. FYI - The standard incandescent bulb's glass temperature in near 200F, the limiting factor for the wattage specification on the fixture, is how much heat the fixture can withstand. The heat will shorten their lives also.
A: No, bulbs are not dimmable.
A: No, it says so right on the box