A: 1. Yes you can build and sell WP themes from epicpxls premium content. We just require to upload those WP themes on our marketplace as well.
2. You can offer the WP theme for free from premium content on epicpxls.

One important note is to not offer the design or the premium items as they are in that product. You can get for example the design and build a WP theme and then sell the code but don't include the design.