The biggest improvement is the amount of memory, which was doubled to the F500-series. The P means it's intended for the European market. There's no Japanese version of the F700.
The F500 and F700 was sold with a mouse and came with the famous Sony KX14-CP1 monitor. This monitor is considered as one of the best monitors for old computers because of the many connectivity options and the superb picture quality thanks to the Trinitron tube.