Yes, it can be manage from the backend Question email notification can be manage from Stores > Configuration > Magediary > Product Questions > Question Email Notification Answer email notification can be manage from Stores > Configuration > Magediary ...
Yes, the admin can set the conditions like show the label only for products which attribute set is Bag or category is Gear. Reference guide: https://magediary.com/docs/product-labels#product-conditions
Yes. In order to show the same question to multiple products, you can assign it to as many products as you want from the backend question edit form. Reference documentation ...
We can add multiple option values by ; separated in the Default Value column under the Form Fields tab. Reference guide: https://magediary.com/docs/product-inquiry-support.html#form-fields