The speedo dropping out and the engine cutting out sounds like the VSS (vehicle speed sensor) could be on its way out. It's located on the gearbox so it may be possible that whilst changing the clutch this has been damaged by the garage. Fairly sure that a 2002 1.8 Mondeo is a blacktop zetec. With some of your spark plug leads being loose, you could have also knackered your coil pack.