How to find source id for an existing collection? + 2 other questions

if a collection already exists and you want to import new works into it - how do you get the collection’s source identifier to use in the CSV?
if our importer is set to recognize ; as a field value separator - can multiple filenames be used in a single file column or does that always need to have multiple columns for multiple files?
in the wiki it says you can separate them by | - is that true if we have configured bulkrax to split on ;?

scientist-softserv / atla-hyku