You'll be so amazed when you discover FontConfig fallback. You can tell freetype to use certain fonts as fallbacks if the font you are using doesn't provide a certain glyph.
Awesome indeed. But oh-my-git is shipped with 3 themes only. So I just stick with their themes. Other methods are way too complicate to fix font issues. All I want is just a font that can be imported into font book or fontforge and let my iTerm2/Terminal to use. That's all.