1. Can I have the same Information Store on more than one Data Flow Diagram (in the same design)?yes, when you create store it appears also in global list "All information stores" - using drag&drop from there you can add it to each data flow diagram. And it'll be the same thing.
2. Can I tell SDDM that an Information Store on a DFD and an Entity on an ERD represent the same concept, and should be linked internally? Ideally in that case, attributes of the Entity and data elements of the Information Store would be forced to be synchronized, or at least I >could run a report telling me whether they were or not (based on name matching).You cannot attach entity to information store saying they are the same concept. Moving of attributes (from logical model) between elements of DFD can be presented with information structures you can create (or use) on Flow - so you create Information structure in flow dialog and add attributes from logical model to it. And data store attributes (entities used) is the set of attributes in information structures of incoming and outgoing flows.