All civilizations that you can embark as are dwarven civilizations, unless the game is modded otherwise.
You can always know a civ is dwarven, of course. Resources are harder; the civ has access to all of the resources that are nearby one of its settlements, but without DFHack you can't actually tell what specific resource types are available. On the other hand, if a civ's settlements are near places with flux stone or aquifers and multiple shallow metals, they're more likely to have access to iron.
Big civilizations have several advantages. They have more settlements, so they're more likely to have access to any particular resource. They have a larger population, which means more variety in the migrants that come (assuming you're on the more recent versions). That larger population also makes it more likely for you to have vampires; always a plus.
You'll never be at war with any dwarven civilization when you play a dwarven civilization. If you didn't embark near your parent civ, however, you're less likely to be near the goblin, human, or elven civs that your civ is at war with, making it take longer for the goblins to attack you in force and less likely that the humans or elves will attack you at all.
Goblins are automatically hostile to dwarves, though that's different from being at war with them. Goblins will always send snatchers, ambush squads, and, eventually sieges, but if you're actually at war with them, they'll siege earlier and ramp up sieges' size faster.
The civ icons on the world map means that they have several settlements in the area whose collective zone of control basically covers the whole world tile. The up shot, again, is that civs with more world tiles controlled have more settlements.