Neither Hearthfire nor Dragonborn interfere with the vanilla game. I don't know what Dawnguard does, I don't have it. I suspect that, like the other plugins, you can kind of ignore it and not have issues. I know Hearthfire doesn't do anything active to the vanilla game unless you decide to buy land and build a house. It does add some alchemical ingredients and some foods for cooking. Once you buy land, the new options come into play.
Dragonborn doesn't do anything to the vanilla game unless you visit the Graybeards and they confirm that you're the dragonborn or unless you go to Windhelm and take a ship to Solstheim. You don't have to do either in which case the Dragonborn stuff is there, just not being used/involved.
Maybe someone else can speak to Dawnguard.
As for running through path to the F&F book, I don't know if it'll work, but I'll definitely give it a try. That would be funny, this orc barbarian with a torch just sprinting past all these lurkers and seekers. There's some really good loot that I'd have to skip...