Cool, I wish the project all the best! Making an interactive historical atlas is a great idea but the path is not an easy one.

We did a similar project and closed it about 5 years ago https://maps.chron.ist/

Had multiple iterations, and put a lot of effort into finding and drawing the maps. Later we found some support from the community and they promised to provide us with verifiable and trusted map sources...

The source code is available here https://github.com/chronhq