interesting that Friday is the fifth day of the week and пять happens to mean 5. Is this on purpose?
Don't know. I suppose there could be a relation between пять and пятница, but probably no direct relation between Friday, Happy Hour, and пьяница. There might also be a relation between четверть and четверг.
There is. Вторник, четверг, and пятница all refer to the second (второй), fourth (четвёртый), and fifth (пятый) days of the week. The word среда (Wednesday) refers to the middle [of the week]. Понедельник (Monday) means "day after do nothing," meaning the day after Sunday, the day of rest. By the way, Sunday, in other Slavic languages, is often some form of "nedele," implying "do nothing," or it may refer to the week in general. The current Russian word for Sunday, воскресенье, is almost identical to the word for "resurrection" (воскресение). Lastly, Saturday (суббота) is simply the Sabbath.
I am curious about понедельник: another comment (which I can not access now -- why is it so hard to get back to these discussions without "following" everything?) said that it comes from "после недели" or "after the week" since it is the first day of the new week.
Right, понедельник means "день после недели", but "неделя" here is an old word for Sunday, so it's "the day after Sunday".