You can upload your media through the Plivo console or via the SMS API.
Plivo supports up to 10 media_urls attachments, as long as the total size of the message body text and all attachments is less than 5MB. An MMS message body can be up to 1,600 characters, which equals 4.8KB or roughly 1% of the total size limit.
If your message (including body text and media) is larger than 5MB, your message will fail with a Plivo error code of 120.