Hi @Eli_Huang,
It sounds like you have the right idea. The best results posing in ZBrush will be achieved by posing the lowest subdivision level of a multi-res mesh with clean quad topology at the base level. The higher resolution the mesh is, the worse it will perform with posing operations, and the more difficult it will be to correct inevitable surface distortion.
ZRemesher is often used to create new low poly topology for this purpose. However it is important to remember that ZRemesher does not fuse geometry. If you feed it two separate meshes, you’ll get two separate meshes back. This may complicate your projection scenario. In addition, Projection is going to work best if the target mesh is a closed solid with a degree of thickness. A wing mesh that is a single piece with a minimal degree of thickness and no 2D areas will give you the best results.
So for the best results here you probably want to make sure the skin stretched between the wings is not a 2D surface, but rather a 3D shape with minimal thickness. Then create a new mesh by merging all the pieces of the wings together with Live Boolean or Dynamesh.
If you Live Boolean the pieces together, it should retain the polygroups of the individual pieces while eliminating any overlapped geometry. Then if you ZRemesh using the “Keep Groups” option, ZRemesher should maintain the polygroups and insert edges where they meet. Now you should have a much higher quality target mesh as a single piece with clean topology that can be subdivded to smooth and to create multiple subdivision levels.
You should have much better results when projecting detail to this mesh. However you may find that you don’t even need to do this. I don’t see a lot of fine surface detail on display in these screenshots, which is typically what you would use projection for. If you don’t have that kind of fine detail, you may find that simply subdividing your new wing mesh to smooth it produces good looking results.
Good luck! 
Any tips?
I’ll look into the Live Boolean method as well–A bit nervous to use Dynamesh haha. Thank you so much for your response!!