I'd say you're doing well at 32 mpgs. At 45 mph I never saw the bright side of 30 mpg, usually 28-29. As for how long it will last, if your car runs well and you take care of it, I would hesitate to say you'd make it to 250 - 300k miles. My 91 Prizm had 319k miles when I sold it, still ran and passed safety inspections.
Then my 2001 Prizm had 220k and my most recent 89 Corolla had over 280k. Gotta love Toyotas.