Yes, the saltwater tank has saltwater in it Aside from that no. Usually saltwater tanks have pre-drilled drains (aka are reef ready) so that a sump can be utilized.
try and get a slightly thicker tank. weight of saltwater is greater than fresh. eg. a used freshwater that's on the thin side, risky to reuse for salt.
Modern Taylor-made Marine systems have bespoke additions inbuilt at the factory. EG, Plenums, Reef shelving, drilled bases to create under-reef water flows etc. They are infinitely more complex than the basic Fresh-water models.
I fail to see any differnce in whether a tank is only FW or SW....If someone can "show" me documentation to disproove this, then by my guest and post it...
A tank is a tank is a tank....glass and sylicon...