By split-ticketing, do you mean buying a separate ticket to get to Nashville once you've arrived in the US? If so, this is a bad idea, since if your first flight is late/delayed, you'll likely forfeit any carrier protection for a later connection. It's also unlikely to be any cheaper. Probably the best place for you to start is to fiddle around with some random dates and city pairs on something like www.kayak.co.uk to get a general idea. Manchester-Nashville is easily doable in a single day with a connecting flight; no need for an airport hotel.

Welcome to FT!