Hi,
You can import closed listings from eBay from the Auctiva Closed Listings page. That can probably help keep you going while you migrate, but the migrated listings won't operate to fullest advantage without template conversion.
In order to migrate templates to Auctiva, you need to look at Auctiva's template tag system, including how that works with Title, Description, Seller Details profiles and selection and placement of pictures. That will give you direction on how to convert your templates to create custom templates in the Auctiva system. A look at any of Auctiva's stock templates will give your coder some basics on how the tags are used. Any of the oldtimers (like me) can give you tips, as well.
I would recommend you view the tutorials and read the FAQ at the HELP link (top of page). It's a very "feature-rich" system, so taking the time to understand the system will definitely reduce cutover work and optimize use (improve productivity).
Danno