Hi Pranav,
I'm afraid Mendix does not support multipart/form-data as valid datatype, so multipart messages are not an option.
You can publish a REST-service operation which accepts binary files to store them as FileDocuments and put some metadata in HTTP-headers, though.
I'm not aware of the possibilities to send the data in chucks, I think the Mendix server is not capable of that. And I'm also not aware of the maximum file size that can be send through a published REST service.
Hopefully this helps a bit.
Kind regards,
Johan