I would say go diesel route. The 1.6 diesel is a great engine economical and performance not to bad.
Get it remapped and it totally transformes the car. It will achieve 60mpg average and make it into a rapid sprinter.
The 1.0 petrol are very thirsty cars once on the motorway.
That's one of the new quad core models, Xda-developers have a load of information on them on their website. The price has come down a little, I paid £227 for mine about 2-3 years ago. I updated mine with custom firmware but it is still a little slow on occasion (especially whilst using the wifi network), when trying to do multiple things.
Mine is one of the older ones but the external case looks the same - the DAB is an external dongle that may or may not be included (check the description carefully) - i'm not sure if it'll plug and play with the Focus antenna but probably will knowing the rest of the wiring is plug and play to the quad-lock connector. The reverse signal is interpreted from the canbus network and there is an option to either get ignition status from the canbus or the ignition terminal in your quadlock (if it's there).