We do not place any restrictions or special requirements on hosting video or audio content or the file sizes used.
Your second example (commercial songs) may pose an issue for you however. Since the use of commercial music could be considered copyright infringement ( I am not a lawyer so I wont comment on fair use vs infringement) you should be aware of how we handle DMCA notices.
If we receive a DMCA notice (for example from a record label who objects to your using one of their songs) we will immediately forward it to you, opening a support ticket on your account. The DMCA requires that we take action. Our support team will follow up with you and will confirm that the infringing content is removed and the reported URLs no longer lead to this content. Repeated DMCA complaints could result in your account being suspended.
With that in mind I would recommend against using commercial content in your podcast without permission as the headaches involved if a label finds your content and reports it is usually not worth the hassle. There is a lot of really good music content out there that is licensed under creative commons licenses allowing their use.
If you do choose to use commercial content I would recommend consulting a lawyer and being prepared to respond if a DMCA is submitted.