I'm not sure I understand what you're asking.
The "fonts as in LRF" approach should work for absolute majority of epubs.
Note that "/Data" is the root of your internal memory (as seen from internal system), you don't have to create "/Data" folder.
Paths are case sensitive.
Do i need serif in end?Whats the difference?
You don't. Difference is "if "LexiaDaMa" is not found, use serif".