A: Hey, here are my responses:
[A] If you want to embed Lunacal calendar in your/clients' websites - the limit is huge. eg. in Tier 3 with 30 users, you can: 1) Create account for 30 clients, each with different calendars, scheduling page, settings etc., 2) Every client can embed their own lunacal calendar in their own websites, so you'll have 30 websites using it, 3) In fact, a single client can create multiple events, and have different calendars for each that they can add to different website pages - a different calendar for partnerships, vs sales, vs careers etc.
[B] Lunacal's own scheduling page can only be done on 1 custom domain (eg. you can select yourself or 1 client for whom lunacal.ai/jeff becomes book.clientdomain.com/jeff. This can be done for all their users) remaining would be on lunacal domain
[C] No, default email language cannot be customised, but we'll solve this very soon
[D] Yes, scheduling page allows any color, theme, language, since it's free text. The calendar language cannot be changed.