To the question of more than one process, the answer is yes. We've set up a slight modification of the jbpm-console and deploy several processes to it. The console is used by users to select the task to perform, perform it, and if the next task can be serviced by them, it is presented. If they have a role that can initiate a specific process, they initiate one.
In a task action, you can provide an upload of a doc. You probably have to persist the path to the doc as a variable in the form, and save the file on the server.
Cheers and good hunting.
Many thanks woo37830!