1 - FreeIPA connectivity is on our to do list. If you actually want to use SavaPage + FreeIPA we can implement it, if you help us test it. Please contact us at email@example.com so we can discuss details.
SavaPage uses one (1) user source for synchronization. So it is not possible to simultaneously connect to one (1) FreeIPA directory and two (2) AD servers from one (1) SavaPage server instance.
2 - If you want SavaPage to be the only access point for printing, you can put your physical printers in a VLAN that can be accessed by SavaPage server only. In this way users will be forced to print to SavaPage first (with generic PostScript driver, or driverless with e.g. file upload), and after that follow one of the many Print Scenarios from within the SavaPage User Web App. Secure Print Release with userid/password, PIN or NFC is possible. You can optionally use a dedicated Custom Proxy Print Release Station positioned next to a printer.
As clustering is concerned: SavaPage is not designed for multiple concurrent server instances behind a dynamic routing (load balancing) proxy. Just a single SavaPage server instance can be active on a database, and on the file system where user data are persisted. As the database part is concerned, this is due to server-side Java/Hibernate caching of database data: concurrent server instances would probably produce SQL constraint violations on unexpected moments. NFS could be used to share file persistence, but again concurrent file access could give conflicts. Above that, HTTP session management and server push messaging will be flawed. Perhaps a fine grained micro-services approach could solve all these issues, but again SavaPage is not designed that way.
The best you can do is implement a static routing scheme where a proxy front-end routes to a single SavaPage server, either being the Primary SavaPage Server or a Fall-back SavaPage Server. Both server instances need to have identical configuration and connect to the same external database (preferably PostgreSQL) and same external user file system. You can use NFS to share the user file system and configure Alternative File Locations in SavaPage accordingly. You can consult this Technical Note where NFS sharing is explained in more detail.