The pitch will effect speed and flight performance depending on style of airplane and engine used. Higher pitch generally produces more speed while less pitch is used more in 3D and scale flight.
Painting the tips of your prop will not only add a cool scale effect, it is a good safety practice to keep from chopping a finger.
A well balanced propeller is a must! Having props that are not properly balanced pose a safety hazard, cause excessive vibration of your model and contribute to poor performance.
A 4-stroke engine produces a more 'scale' sound while providing better gas effeciency and more torque for bigger propellers. Excellent for adding realism to your larger airplanes.
A 2-stroke engine runs at a higher RPM while producing less torque but better power-to-weight ratio. Great for smaller fast airplanes.