As far as I know there is no rule about how many you can cross-cover, but there should be IMHO.
Covering BOTH the unit and the floor is a really, really bad idea for one resident.
I mean I can see scenarios where it might work, smaller hospital + small bed unit, where the total crosscover pateints was, I don't know, half of what the OP was talking about.
It really sucks what the new and "improved' work hours have done to us. Of course bring some sanity to no restrictions and 120hr weeks was sane and humane, but the newest "fix" has been really bad all around. I finished my residency before these new hours, and every night we had two floor interns cross covering the floor, a supervising resident admitting to the floor, and an ICU resident covering and admitting to the unit, with both the cards and pulm fellow very accessable from home. I guess my bias is for something similar.