2 - Why is electron charge negative? How many unnecessary minus signs has this poor choice caused?
Because the person who decided the sign didn't have a way of knowing a priori whether the stuff that was moving from rod to fur and from rod to silk was numerically a particular kind of charge carrier flowing in a particular kind of direction. At the point you're rubbing a piece of silk on a glass rod, you know some transfer is happening to make the silk attract the fur, but you don't know whether you're rubbing something off of the rod or onto the rod.
Because the person who decided the sign didn't have a way of knowing a priori whether the stuff that was moving from rod to fur and from rod to silk was numerically a particular kind of charge carrier flowing in a particular kind of direction. At the point you're rubbing a piece of silk on a glass rod, you know some transfer is happening to make the silk attract the fur, but you don't know whether you're rubbing something off of the rod or onto the rod.