Using a single passphrase to unlock multiple encrypted disks at boot

My machine has an SSD, where I installed the system and an HDD, which I use as a storage for large and/or infrequently used files. Both are encrypted, but I chose to use the same passphrase for them. SSD is mounted at / and HDD at /usr/hdd (individual users each have a directory on it and can symlink as they like from home directory).

How can I install Debian with full-disk encryption and a custom sized swapfile?

I’m trying to use a Debian network cd to install it, via the advanced graphical installer. I want to use the full-disk encryption option, but I’m trying to install it on an older machine. I think it has about 1GB of RAM. I installed Pop!_OS on it, and it ran fast enough, as I could specify a decent swapfile size, but try as I might, I couldn’t get it to find a graphics driver that would give me anything but a 640 screen resolution. (Debian found a great video driver, FWIW).