As you have said, we have a few different options if you want a mirror installation. We recommend GBiB (https://genome.ucsc.edu/goldenPath/help/gbib.html) as the simplest method, it's a self-contained virtual machine containing a functional Genome Browser.
GBiC is another solution, when you would like to install a mirror on your own machine, or cloud instance.
The GBiC installation (as well as the GBiB) can be quite large. Both of these can be installed with a minimal amount of data, and then they will query the Genome Browser servers live on demand as more data is explored. This minimal installation, depending on settings and assemblies, can be up to 1-2TB, though often less.
In our help docs we do cover the scenario when your partition is too small, see Root file system too small for all data.
If you need to move data to another partition because the root file
system is too small for all of the assembly's data, the following
steps will help complete the installation. First, create the following
directories and then make symlinks to the directory that will contain
ln -s /home/xxx/storage1/mysql /var/lib/mysql
ln -s /home/xxx/storage1/gbdb /gbdb
If you have any follow up questions, our help desk can always be reached at email@example.com. You may also send questions to firstname.lastname@example.org if they contain sensitive data. For any Genome Browser questions on Biostars, the UCSC tag is the best way to ensure visibility by the team.