Suspension? What should I expect from this van?

Some of those components would be typical at that age and mileage. Replacing half shafts in pairs is not a common practice. I have seen one fail and the other last for thousands of miles, so it is typically done on an as need basis.

Replace the shocks.

The rear brakes are drum brakes it is possible the noise is brake dust inside the drum or inferior quality brake linings, has someone inspected the rear brakes to see the brakes are functional and safe. It does sound like the shocks may be worn. These are great vans I wonder if this vehicle just had a hard life before you bought it. Have you records for previous service history and or a timing belt having been done. The vibration you mention, are the tires and rims in good condition. Tires in balance, rims in good order. The brake discs and drums may need to be checked for "true/run out".