Merge 2D background with 3D Character

Hello,

Are there any ressources, tutorial or workflow to reach an approching resultat like that : http://www.siliconera.com/postgallery/?p_gal=196796|1 It uses 2D hand painted background and 3D characters.

I've spend hours dealing with orthographic camera with Isometric angle : (30,45,0) and textures added to transparent planes (with differents shader transparency queues)and oriented to face camera but I don't thing its the best way...

Should I use a plugin like 2D toolkit or other ?

Best regards