Yeah, arc-dodging is quite literally that.
As i understand it, the game has three core ship types: Turret, jouster, arc-dodger. They have kind of rock-paper-scissors balance but this is not a hard rule.
Turret ships just chip away at the enemy. Twin-laser turret armed Y-Wings are a good example. They counter arc-dodgers.
Jousters are kinda tough, frontal assault ships. The (T-70) X-wing is one in principle. You just flip around (K-turn) and attack again. They counter turrets, as turrets may have poor mobility and lack firepower.
Arc-dodgers are maneuverable and powerful but can't take hits, hence avoidance of firing arcs. They counter jousters with their maneuverability.
In addition to these, there are "bombers" and "supports" that don't quite fit any of these categories, and as ships may overlap other roles. The K-wing for example, can be a turret or a bomber or both (though using points for both is not necessarily wise). A Lambda shuttle with Emperor Palpatine would be an example of support.
Trying everything is a good idea for sure. I am myself currently focusing on broadening my mini selection rather than getting more what i like. And the E-wing is on my list though low priority. For casual gaming it is probably good enough. I did advocate the HWK-260 earlier, a ship many see as a poor ship...
As for double packs, they are often about fixing or improving weaker ships. Imperial Veterans adds options for the TIE Bomber (like turning it into a support ship with TIE Shuttle title) and buffs TIE Defender considerably with the title options (TIE/D and TIE/7x). If you really want to play with certain ships, you may well want those double packs. They do come with good cards often in any case, and that maybe good reason to get them (unless you just print cards or proxy them).