1. Blueberries; Yes two different cultivars helps. Also you mentioned
South Carolina, unless you are very upstate, you will need either
rabbiteyes (type) or southern highbush. The northern highbush just
does not do much in the higher USDA zones. All blueberries need an
acidic soil pH (5.5 -5.5) Most Georgia and South Carolina soils are
naturally acid, but yours has probably been limed. Take a soil sample
to you extension agent. The liquid iron sulfate (soil acidifier) sold
at most nurseries is the quickest and easiest way to lower pH.

2. Raspberries and blackberries do not naturally cross, But
raspberries do vector diseases that take out blackberries. Not a good
idea to plant the close together.

3. Cherries are difficult in this part of the country. They are also
very slow growing. It will be quite a few years before you find out
what your seedlings will do.

4. The same iron sulfate as on the blueberries