Hey Jim,
For the first scenario, you'll want to partition your list between existing leads, and leads imported with the list. To do this, you will need to create two static lists prior to import your CSV. One should be called "All leads [List Name]" and the other should be "New Leads from [List Name]." You'll then need to set up a smart campaign with a Lead is created trigger, and the Constraint List Name is "All Leads [List Name]" then a Flow of "Add to List - New Leads." When you import your list into the all leads static list, this will move any leads created by this import operation into the new leads list, allowing you to partition them out, and suspend marketing after communication.
For the second scenario, it's typical to set up a trigger campaign to remove Marketing Suspended. Usually this is based on a Form Fillout, but other forms of engagement may be appropriate.