Re the two pumps to equalize, I agree with your assesment that is too difficult. One float switch breaks and its no longer redundant but rather the cause for water on the floor. And much the same as I would type to someone considering a sump, at that point the effort is better made considering some overflow or drilling or finding some mechanical saftey less likely to break. I think your last ideas are good and you don't need this newest idea. Just 2 cents of course.
Great diagrams by the way and very easy to follow.
Great diagrams by the way and very easy to follow.