Where can i find some decent resources,tutorials on how to use multiple blend files to save RAM usage in BGE? As far as i know, even if i use overlay scenes, the objects are still in memory.
Multiple blendfiles are more a way to manage your project & content, they wont save ram since blender loads them all into memory anyway.
Any docs you can find on blenders linked libs and dupligroups will help since you can use dupligroups in blender since 2.48