Short answer: **Inaccessible
Long answer: Discord's API does not allow me to receive the Nitro status of an user. The requested user would have to authorize Discord.ID (Oauth2, like when you add a Bot) in order to get the information.
No. This is not supported by Discord and also against a core value of mine: Privacy.
No. Beside some technical impossiblities, it's not what discord.id should be about.
No. This is technically not possible nor supported by Discord.
Yes. Use it and don't try to use discord.id as an API.