throttle bodies are essentially a throttle for each cylinder, and look like a twin carbrettor conversion, but are more modern and use fuel injection,

if you search for ades mk4 escort estate on here he has fitted throttle bodies to the engine in his car. iirc he gained around 40bhp and they sounded amazing. but cost around £1000+

these will replace your whole inlet system right up to the actual head, so personally i would decide what you want from the car, (power wise and in the futue) before deciding on this mod.

as for the airbox mod, this can be done simply by getting an airbox and some ducting, drill a hole in the bottom of the airbox and place the end of the ducting inside with the other end pointing somewhere where it will receive cold air (front bumper ideally)

and you could also buy some exhaust temprate reducing paint to loose some under bonnet temps