Yes I'd forgotten about the USS Montgomery, dunitall. Other sights to behold from the coast of Sheppey are the power station on the Isle of Grain and, across the estuary, the gas terminal near Canvey Island. If you really want a thrill there is the car import terminal just near Sheerness.
If you want to cross the channel, sherrardk, you will have to go from Dover. (The passenger ferry service from Sheerness to Flushing ceased some years ago). This is a journey of around 50 miles and will take you a good hour down the M2/A2. My recommendation would be to stay somewhere along the north Kent coast, say Whitstable or Herne Bay. Ramsgate is an "improving" town these days (certainly better than anywhere on Sheppey) and it has a good beach and one or two half decent pubs and restaurants. In the area the Battle of Britain museum at Manston, Dover Castle (allow a whole day), the narrow gauge Romney, Hythe and Dymchurch Railway (a delight) and the City of Canterbury are not too far away. Apart from being a bit of a dump, Sheppey is not really convenient for other parts of Kent and I cannot recommend it at all.