We'd love for you to give Auctiva a try! To answer your questions:
1. Yes, and it can be customized or you can use our default invoice/payment reminder email.
2. Yes, we allow custom template creation (you can paste the html from your six-bit templates into Auctiva) or you can select one of our new mobile responsive, active-content free/ebay compliant templates and customize it to meet your needs.
If you run into any issues or have quesitons, please don't hesitate to reach out to our Support team, they are here and happy to help! https://www.auctiva.com/help/requesthelp.aspx