Does every product need to be assigned to an email template?

No, products that are not assigned will not have these additional emails sent for them.

If I assign products to an email template will I/the customer still receive confirmation emails?

Yes, participation in these email templates will not affect the customer or business order confirmation emails in any way.

Can a product be assigned to more than one email template?

Yes, you can assign a product to multiple email templates.

Can I assign a product to use multiple emails of the same type?

Yes, a product can be assigned to multiple emails of the same type. 

If a customer buys two products both with the same email template assigned will they receive it twice?

No, each email template will only be sent once per transaction. However, if you have multiple email template types assigned, for example a pre-activity for rafting and a pre-activity for hiking, and a customer purchases both, they will receive both pre-activity emails in this situation.

Can I use this for marketing emails?

No, these emails should only be related to a transaction and as such restrictions have been put in place to maintain that standard.