Baseplate

I am thinking of buying an opened Lego 8420 set. It has two unopened bags in the box, and I'm wondering if that is all or if there were more. Also, both tires and wheels are missing, so does anyone know where I could find those for sale. I searched ebay and Google, but I did not find any for sale. (Bricklink is also down for daily maintenance at the time I am posting this.)The tire and wheel part numbers are 51379 and 51378 respectively. Furthermore, will any other more common motorcycle wheels from sets such as 8051 work on this set? Thanks.

Thank you all very much for the information.