Good Afternoon Fernando.
Catalog (and USS too) has no available limit for the amount of attachments you can add to a request.
The only limitation you can configure is to set an offering with 'Attachment Mandatory'.
In order to ask for an attachment before the service is requested.
Once an attachments is added, you can have 2, 3 or more, and the condition will be fulfilled (Attachments != 0).
Thanks and kind regards, Louis.