Hi cmmm,
1. If you already have a paid D365CE instance in use, then you can integrate Marketing with your instance by adding a Marketing app to your tenant and then assigning it to the appropriate instance. For more situations, please read it.
2. Yes, it has independent database from D365CE and a individual instance. D365 Marketing is licensed per instance, with each instance priced according to the number of marketing contacts stored in your database.
3. It depends on what type(standalone or included) of marketing application, there is no requirement for D365CE license if it's standalone.
To receive the “included” Marketing Application, customers must have and maintain at least 10 full users of D365CE or D365 Plans, please read this license guide.
You could request a free trial here.
Regards,
Clofly
