No. Washing the bag in a washing machine will cause the fill to lose its insulating factor. Best thing to do is unzip and let air out, then spray with an anti microbial spray. The outer shell can be wiped down with a damp cloth.
-20 degrees Fahrenheit. It worked pretty well even at those temps. I don't recommend trying it though. I have used the bag in 0 degree weather also and was comfortable. Pretty nice sleeping bag for the price!
The Zipper only runs down the side of the Sleeping bag, if you wanted to zip another sleeping bag to it you would have to purchace the opposing side, in other words there is a left and a right, to dangle your legs out, you could do it out the side of the bag, not the bottom, hope this helps.....
Hard to say. Every time the inside of the bag got wet from outside moisture, it came through the corners where the stitching is. The thread and zipper seem to wick the moisture into the inside of the bag. I have never camped outside of a tent with it, with no cover.