Well, you got the answers you were looking for, here is a different answer. To your other implied question, how to not worry about dust getting in other holes.
Main thing is to develop positive air pressure. You want more powered intake than powered exhaust.
Use fans for all your filtered air intakes, ignore powered air exhaust, run it at lower fan speeds if you can. Air will get out fine. If you force the air in where you want it to go in, dust will only go into the easily removable filters, it won't be on your components. Any extra hole in the case will just be exhausting the already filtered air. Then just remember to actually check and clean your filters. That's the hard part. But if you clean them when they need to be cleaned, you will never have to actually clean the inside or the fans or components or anything else, just the filters.
Nowadays, it is exactly as complex as it sounds. There is a ton of blending, pitch and playrate tweaking, separate modifiers for current rpm and how much the accelerator is currently depressed. And yeah, like hundreds of recorded samples from the real car when possible, or a similar sounding car when not possible.
We are probably on the verge of getting to a point where a rough simulation might soon be able to take over for this process. It won't sound as good for a while still, but it will be cheaper and faster soon. And as time goes on, it'll get close enough to sounding right while continuing to decrease in cost and time taken to a point where it'll be the only way to do it eventually