Yea i can see duplicating being annoying but i sadly can't make the sharing work quickly because of the way C2 and my plugin use different canvas contexts, doubly prevented by the fact the sdk doesn't make these types of things too easy (theres no convenient way to share it). I'll look into ways to hack around it if possible but i don't have too much time to make big changes atm.
Even if you have duplicate textures, i think (you'd have to ask Ashley to make sure) that on export C2 detects duplicates and doesn't make copies, so file size would be the same, the only disadvantage is the annoyance of importing twice while working.
you don't need to do anything extra for q3d model to have animated textures as i explained, it just animates it if there are multiple frames / animation speed etc.. you can even change animation for the map types like you would sprites.
I could add a Q3D sprite option for a plane, but the issue is it becomes kind of redundant since it can be done with Q3D Model already, and it can interact with lights and have normal maps on top of that so it's just all around better to use, if you dont want lighting you could just select "basic" as the material type.
If you don't want to create a plane model (although you could just do this once anyway), theres a "advanced" feature i talk about in the recent changelog that you can use to create a plane geometry internally to use. Just make an action for q3d master that creates a plane using the "plane" action in the 'geometry' section, choose a name like "MyPlane" for the geometry, then on a q3d model using it's property for "model filename", the same way you'd load a model write "MyPlane.geom" and it'll load a plane (or whatever type of geometry you have) the ".geom" tells it the name is an internally created geometry. you can use this to load any of the stuff you can create using the actions in the section, which can come in handy for mocking stuff up quickly without opening > exporting etc.
If im not clear enough please let me know! i'll do my best to help.
A lot of these features aren't obvious but im trying to work on documentation that covers everything