A: Hi tampan!
1. We use BunnyCDN to power the Easy IO "edge".
2. You can definitely use it for non-WordPress sites, though we don't have any direct integrations outside WP. You can request other platforms, or use our PHP tools to build your own:
https://github.com/nosilver4u/ewwwio-silo
https://github.com/nosilver4u/ewwwio-php
3. Indeed EWWW IO does work well with both of those, and we work with the WP Rocket team periodically on any compatibility issues that arise. *Though I'd recommend trying out the SWIS Performance plugin included with this bundle, you might not need WP Rocket anymore.