Optimum setup for Truenas Scale on Mini XL Plus

[TrueNaut]

I've recently got my TrueNAS Mini XL Plus, and have 4 18TB drives set up in a RAIDZ2 configuration. The boot pool is hosted on the included 500GB NVMe drive. My goal is to install multiple apps and improve read and write speeds. To achieve this, I'm considering adding two 1TB SSD drives. Could you kindly provide guidance on the best approach for app installation, caching etc? Should I use SSDs for this purpose? Additionally, I'm curious about caching. Is it possible to use one SSD for caching and the other for apps? Your expert advice on the optimum setup would be greatly appreciated.