videos API domain limit

i have a gold membership and it says there is a limit of 1,000 domains for the videos API.
Can i get a bit more detailed breakdown on this ?

If I followed the instructions to enable all subdomains of a multisite, do these subdomains count in the 1,000 limit ? if a thousand sites on multisite still counts as 1 limit, will this still be the case if the user uses domain mapping ?

Can I use the plugin in a multisite for all domains as well as a separate single WP site ? (in that case I would have to install plugin for that site ?) separately as well registering that site in my "Support Videos API" section for it to work ?

kind regards,