@Matt Venn: Take a look at the "Install" page for open_pdks. You don't need to install every submodule of skywater-pdk, and in particular for analog design, you probably don't need any digital standard cells other than sky130_fd_sc_hd (the most common) and sky130_fd_sc_hvl (in case the digital is driving 3.3V to 5.5V analog). The liberty files for the digital standard cells is what takes up all the disk space. Cleaning up or deleting the skywater-pdk repository after installing open_pdks will recover a lot of space, too, since those massive liberty files are just copied from skywater-pdk into the open_pdks space.
The most critical submodule for analog design is sky130_fd_pr.