Shouldn't this be "An airplane is very expensive"? "too expensive" would be "demais caro"?
Yes, you are right. But demais comes after the adjective, so you say caro demais
Muito can be very or too, depending on which intonation you give to the sentence.
What's the difference between avião and aeroplano?
avião involves all kinds of planes and aeroplano is specific, a small kind of plane. If you enter Google you can see pictures of it! ;)
Oh man this reader lady... Isn't one r in the middle of the word supposed to be silent/H? She definitely says a clear R sound. Not that muito carro makes much sense... :P
Two Rs are pronounced like an H.