1. Any mob that has a ^ above it is harder, but it is not necesarily heroic. Heroics will usually be ^^^ or a few ^^ or a large group of ^ that are all grouped together. You can tell if a mob is heroic when you target it. The default UI will show you the brakets and under the mob name it will say Heroic if it is a heroic mob.
2. Just having a name will usually make a mob a bit harder. However there are solo names just like here are heroic names. The solo names are a lot easier and drop less rewards than the heroic names. The heroic names are designed for a group rather than an individual.
3. I'm not really sure what the brakets mean, although mobs with them seem to be a bit harder.
4. A mob does not need to be heroic to be named, but all named do not have a guarantee to drop a chest. Heroic named have a much better chance of dropping a high quality chest than a regular heroic. Some named mobs are there for specific quests and do not drop any chests at all. I expect that is to deter farmers from taking out quest mobs and preventing people from completing their quests.