Questions about assetbundle and memory management

I'm trying to use assetbundle with dependency.The problem is that when I load a prefab in a bundle,I must load the bundle containing dependencies first.Currently I just pack all the resouces to sevaral big bundles,like texture bundle and model bundle.I load all the assetbundles when the game starts and dont't unload them until the game is about to quit.

My question is,if I don't call the loadAll() function,how much memory will the assetbundles cost?Because I found it's not necessary to call loadAll() if the bundle is just referenced by others.In this way can I load all the assetbundles at the beginning,so I don't have to take care about the dependency relationships between each bundle?

Other question is,If i don't unload the assetbundle,can I use the Resources.UnloadUnusedAssets() to unload the assets loaded by assetbundle?