Yes, you can upload your company Logo. Goto Setup > Admin Setup > Company Details> edit and upload your logo. Please check the image size before you upload.
Primary Contact is the person to whom all the alerts, related to Subscription are sent. Please make sure Primary Contact information is updated with the current information.
Yes, you can update a particular field using WorkFlow Assignment Values. Goto Setup > Workflow Settings > Create a workflow rule. Then create a workflow assignment value and associate that to the Workflow Rule. For detailed help to create workflow ...