To open Hearthfire you need to register the BSA file in the skyrimeditor.ini by adding hearthfire.bsa to the [Archive] section by adding it to this line :
SResourceArchiveList2=Skyrim - Shaders.bsa, Update.bsa, Dawnguard.bsa, Hearthfires.bsa
That should take care of the BSGLocalizedString.cpp error and Crash
Then to load more than one master file you need to add this line to the [General] section of the same ini file :
bAllowMultipleMasterLoads=1
And that should fix the first error