To be honest Fallout New Vegas isn't about the mainplot. It is pretty much the worst questline in the whole game. As in almost all other Fallout games. Just run straight into the world and into whichever direction you'd like to. It doesn't matter. Just try not to kill named NPCs just for the hell of it, or you might break some quests later on. The fallout series is a true embodiment of the term "open world". You can run around aimlessly, you can chart the whole world map systematically, or you can just talk to the very next named NPC and probably will embark on a journey through half of the worldmap anyway.
Your best bet is ignoring the main plot and leaving that for last.