The Bosendorfer library is 400mb and I'm deleting it. Hopefully I'll have a lot more space.

Hello Adrian - if you mean you have 8 nlibraries loaded into Montage (the maximum) there is no need to delete any of them - save them to a decent sized USB key instead (I use a 16Gb) - preferably a separate one to that you use for updates. Once they're safely on the USB you can delete them from Montage. The alternative is to convert Libraries into User files, which you need to do if you are to make lasting changes to them, then delete that Library so that you can add another. It is a little confusing as to what is where, so you need to keep track of what you've done!

Question 1
I'm trying to load some new voices that I've made but I'm getting a memory full message. I guess I have to delete some of the other libraries which I had installed.

However, how can see what performances I'd like to keep and those I can delete? Is that even possible?

Question 2
Can I load a voice (.x3v file) directly onto the Montage which I created using samples? Or will I need to create a .x3a file with all the voices and the load the .x3a file as a library

A Motif XF All Voice file (.X3V) can be loaded to the Montage USER Bank or can be installed directly to an available LIBRARY Bank location (provided you have room available).

If you load them to the USER Bank, they will occupy 544 out of 640 User Performances. You can play through them as follows:
From the Performance (Home) screen
Press [CATEGORY SEARCH]
Set MAIN = All
Touch "Bank" > select "User"
The listing will show just the Performances created when Montage converted the 544 Voices to 544 Single Part Montage Performances.
You can play through them - one after another... either from the Search screen or return to the HOME screen and use the [INC] button or Data Dial to advance through them.

If you don't wish to keep a converted User Performance (either because it duplicates one already in the Montage, or you just don't want to keep it) you can navigate to the User Performance Utility FOLDER and DELETE the Performance
Press [UTILITY]
Touch "Contents" > "Data Utility" > touch the Folder "Performance"

Here you can manage your User Bank Performances as you require. The idea is to have just the Data you wish to keep in the User Bank... then you can create a NEW Montage LIBRARY File (.X7L) from the data currently in your User Bank.