Not sure this is the correct channel to ask, however, currently from my knowledge there is one field on a Customer record "email" that is used by default for all transactional emails such as Invoice, Quote, Order.
1. Is that correct?
2. Is the a bundle/mod that is commonly used to allow for having a email field for each of these transactions?
3. If there is no bundle/mod that is common is it advised to utilize custom scripting or am I walking into a mess?