First off: great work! It looks like you’re really serious about building an effective DIY air purifier. Pressure drop data for a HEPA filter can help you find a suitable fan and calculate a rough approximation of the airflow (albeit not CADR) of the purifier.
Unfortunately, however, we do not have pressure drop values available for our HEPA filters for different airflows and/or fan configurations. To provide these would require us to test each HEPA filter for different fan and airflow configurations.
General pressure drop values for HEPA filters
Having said this, a rough approximation is that in our testing, most Smart Air HEPA filters have a pressure drop of between 50-200Pa, depending on the airflow, air duct and how clogged the filter is. This can be used as a rough range to find and size a fan.