For my pedals I took some measurements of my feet in the shoes I like to drive in. With you heel on the floor measure the height to the ball of your foot. A little higher than that is where you brake and clutch pedal should be. The ball of your foot does the pushing and you need a little clearance between your heel and the floor when on the pedal.
The width is a problem as the foot boxes are fairly narrow. Again pull out the tape measure and with your feet together measure the distance between the balls of your feet. Space the pedals a bit further than that apart so you have enough room between your feet on the pedals so they don't clash as you press the clutch. Also give yourself enough room on the left side of the clutch so you can slip your foot past to give your leg a rest.
The gas pedal is personal preference. Some people heel toe so with the ball of you foot on the brake the bottom of the gas pedal needs to be close enough you can hit it with your heel but not get in the way when you jump on the brake pedal. Some like to use the side of their foot on the gas pedal so it needs to be close enough to hit it.
Here's my pedals bent to where I find them comfortable.
The Gas pedal however is easily adjustable. You can move the tread up and down depending on which set of holes you bolt it to. You can also pivot it left and right as it's on a threaded mounting and you can change the pedal height without changing the pedal throw by turning the pedal out the required number of threads.
There's also a back stop on the pedal that is adjustable. I thought this was important as you don't want to be stretching the throttle cable at wide open throttle.
Cheers