Help with partitioning for Kali + DracOS dual-boot on 2012 MacBook Pro

I have a 2012 MacBook Pro with a 1TB hard drive from a 2015 iMac. It has two 4GB RAM sticks; one originally came with this MacBook Pro, and the other is from an older HP laptop. There are no residual traces of macOS on the machine. This is approximately the fourth time I’ve installed Kali Linux, gradually fine-tuning everything each time. This time, however, I’m installing Kali in legacy mode to gain more control over the BIOS (ring -2). I only install OSes to load directly into root (ring 0), eliminating the home (ring 3) section of partitioning. As someone who enjoys pushing limits and designing unique setups, I want this machine to support dual-booting two separate OSes (only one running at a time), selectable at power-on. I want Kali Linux to be fully operational, but I also want to install DracOS with a custom Nix toolbox. I’ve never installed two OSes on one machine before and want to ensure partitioning is done correctly. I’m currently in the partition setup via Kali Linux graphical expert mode. Thank you for taking the time to read and review my questions and for any guidance you can provide.