[Koha] A couple of questions about Koha

Hi group, I am new to the list and helping a non-profit organization out that is using Koha. I have a couple of questions. Is it possible to have polyhierarchy in Koha? They have some materials that don't categorize in one place very well. Also, I noticed that it looks like you can import a collection into Koha. Right now the organization's holdings are in an Excel spreadsheet. What needs to happen to the data before it can be migrated? Thanks, Christine