If BizTalk is polling and processing messages from various receive locations, will it process multiple messages at the same time or does it work through the messages one by one? Some of these messages will be in excess of 8MB so will take some time to process.
BizTalk, by design, will handle incoming messages in parallel. In fact it’s tricky to make BizTalk handle just one document at a time (but it can be done).
But my recommendation is to let BizTalk do it’s stuff. Set up a test which will stress this aspect of your app, and then if there are problems, introduce some kind of throttling technique. But to start with just let BizTalk handle the problem itself.