I think the problem with docking ships together was figuring out what to do with all the solar arrays so they don't overlap each other. This issue was discussed previously, but I haven't found the thread yet.I do think formation flying should be possible. They would need to do Mars injection burns at close intervals, but not necessarily at the same time.
Bad idea to spin them or try to create artificial gravity. Creates a bunch of problems and barely gives any benefits. Remember that Elon wants to send ITS on fast trajectories, so even less reason than usual to do it on a Mars mission.
If they end up flying docked together to Mars, or even near each other. They are going to be arriving at the same time. This means that either they will be flying in close proximity during the EDL, which is dangerous. Or they will be landing far apart, which I assume is not the intended goal. (I imagine they'll all want to land at the same base.)Flying together could involve a 90 minute separation between TMI of ships though. To allow for some sort of contingency, but there's no reason to do it for luxurious reasons such as dedicated dining rooms.
Regarding a squadron of ITS arriving at the same time. Is there a showstopper reason why they can't aerobrake but then pop back up into a stable Mars orbit such that they can then choose a good time to land?
I mean use aerobraking to slow down enough that you stay in orbit but not enough that you have to land. Dip into atmosphere, slow down enough to no longer be able to leave Mars orbit, but not so much that you have to land. In other words using very little fuel if any at all.