I would like to move /usr to a different partition because I would like to not use that much space on my ssd in favor of my fairly empty hdd. I would also like to move another /snap since it eats up alot of space as well. I know I could just physically move it but would all the programs that use it automatically be updated to point towards the new directory? Will new applications still go to the moved /usr or would it create a new one on the SSD and use that again? On ver 5.0.
Moving the directory to a different partition won't work. The best solution would probably be to do this during the installation process.
You need to create 3 separate partitions, 1 on the SSD with
/ mountpoint and the other two on the hard drive with mount points
It is also a good practise to have
/home directory on a separate partion, it helps a lot when reinstalling os or changing a linux distro. And it's also good to have a Swap partition.
I wouldn't recommend doing this on a running system.
For more info on this you can see https://wiki.archlinux.org/index.php/partitioning#Partition_scheme