Both the style and purpose of Spirit of Innovation remind me of the Mew Gull, a pre war King’s Races winner with the side goal of beating the Luftwaffe to having the fastest aircraft:
What's the all-important figure: Maximum flight distance?
In practice though, it's maximum minutes as many planes will be taxiing then need to sit on the tarmac for quite a while waiting for take-off, and taxiing and loitering after landing till it can reach the terminal.
For the motor: A lot more insulation on the coil windings mostly. Higher voltage usually means less copper needed and more insulation. Boosting voltage from batteries is pretty easy. Either using a transformer on the motor controller or putting enough cells in series to get the voltage you want. There are also methods using inductors and PWM to get a boosted voltage.
The same way as any other battery, just increase the number of cells. Most cells seem to run between 1.5-2 volts. A 12 volt car battery is usually six cells of 2 volts each.
Most noise from prop planes comes from the propeller. You can make some pretty quiet prop planes though. Especially if you use lots of smaller propellers. However for a race plane you can bet this thing is loud as heck.
https://en.m.wikipedia.org/wiki/Percival_Mew_Gull