It depends on the year. 1989 - 1994 Geo Metros will usually get 35mpg city/50 mpg Highway. 1995 - 2001 will get anywhere from 30mpg city/ 45 mpg highway. If you have the super rare 1991 - 1994 Geo Metro XFI that I have you can get up to 60 mpg. These are all based on Geo Metros with stickshifts.
Many of the parts will interchange. Some of the interior parts, especially around the dash board are different. Also, under the hood, electrical components and fuel components will be different. What specifically are you looking for? Mr Geo Metro firstname.lastname@example.org
Yes it will. from 1989 - 1995 all geo metros (as well as Suzuki Swift) had the same engines. As long as they both have the same type of transmission and the same size (1.0) it will fit. Hope this helps.