Some question regarding engine, transmission

[squid]

it's going to be very hard to change the ratios in your car, and i doubt anyone makes any aftermarket gearsets for it.
your only option would be to do a manual conversion if that has better ratios.
you could turbo this car, but the engine internals probably wouldn't handle it, and it would probably cost more than the car. even if you doubled the power, you'd still only have 90kw.
there are some fun kei cars out there, like the suzuki cappucino, Mazda AZ-1, or the suzuki alto works rs-r, and they are already turbo so it's a lot easier to get more power out of them