There isn't a limit to the number of plugins you can use with a child theme (but you can only use one child theme on an installation), however you may wish to check with the child theme developer if the products are compatible with their child theme. You can communicate with the child theme developer in the "comments" section of their product page
here. Note also, that you still need to purchase the
Vantage theme itself if you plan to use the Directory child theme (you cannot use the child theme without the parent). Thanks.