I don't think there's any difference. "Egy piros autót várok." means the same.

It is correct, please report it.

I very much assume the Hungarians got this expression from us. :´)

Same in Czech. Viva la Austro-Hungarian Empire! :D

Standard English is 'wait for', not 'wait on'. But you do hear 'wait on' in some dialects in casual speech.

I assume in Hungarian if you were to 'wait on' the car, you are already sitting on the roof of the car and waiting for something else. This sentence implies that it's the car you're waiting for.

Meaning that you're sitting on it? It seems to be incorrect because "-ra" would imply movement (although here it works specifically with "vár").

Both are possible.

"What do you do every morning? -- I wait for a red car."