re: If Europa's global liquid water ocean is 60 miles deep...
I still say the best bet for a Europa probe is to start with an orbiter than can really nail down what's happening on the surface. It's very likely that they will find areas where deep-down water has been expelled to the surface, and perhaps recently.
Land a probe there. Preferably a rover. If you do it right, the orbiter brought it along. Maybe several of them. To get possible biosamples from any deep ocean, they just need to dig deep enough to get at new geyser ice shielded from the radiation. If they find a frozen carp, all the better.