There are no official ways to partition the boot drive. It is also highly recommended against to do so.
The boot drive is seen as a throw away device. If it fails simply reinstall and restore with the config file (have always one saved somewhere).
You most likely will not benefit from any “cache” drives. In ZFS your RAM is your primary cache.
So use 1 cheap and small ssd as your boot device and 1-2 SSDs for Apps and VMs.