I would use 1:43 for your cars and pick-up trucks, and 1:50 for your box trucks, tractor-trailer trucks and buses. There are many choices in these scales. All of the many cars and trucks I have on my layout are in these respective scales, and they all look great. My favorite brands are as follows: Matchbox and Road Champs for the cars and pick-up trucks, Athearn for the box trucks, Corgi and Lionel for the tractor-trailer trucks, and Corgi for the buses. All of these are relatively inexpensive. In my opinion, there is no need to buy the very expensive brands. Better to spend the money on trains.