3 – I could let both ballscrews be driven from the same motor but I guess that would require a belt and with that I would loose some of the precision.
This is one of the standard ways of doing this and has been proved to work well. If you look through the forum there are many cases where it has been done this way.

Installing a second switch as your point (1) will not work. Point (2) Will work as Jazzcnc has already said (but it is not an elegant way of doing it). Not sure what you mean in point (5) it has nothing to do with the homing sequence