I own a 02 model exis.
fuel avg (petrol)
city around 11 km/l
highway around 19 km/l if u drive @ 120 kmh.
CNG :
city : i'm getting like 160-170 km/cylinder.
highway : around 190 km.
maintenance :
Air-filter : 250-350.
oil filter : 120-150
She takes 3.7 litres of oil.
Other then that, most parts can be sourced from 2nd hard car market like shersha if not found new.
Performance :
Well she is one of the fastest in it's category with very effective road grip.But suspension is a bit hard (because she has kinda sports suspension) when compared to later models.
If u r above or close to 6 ft' in height then u might have problem while sitting on driving seat because the gap between seat and steering is a bit less.also the steering is not adjustable.
And lastly, engine over hauling...well as per honda it's engine needs over hauling after 500k kms if not abused.