Here is my question rephrased. I don't know exactly how to texture in blender. I've got a rifle I made in blender. I made it entirely out of one cube. When I brought it into unity, there was no way for me to texture the weapon individual textures. Like the handle flat black and the stock a wood grain spec diffuse. I was only able to texture the weapon in unity in one texture. My question is, is it better to go from edit mode to object mode in blender to create individual pieces of the weapon so that when it's exported to unity i'm able to texture those individual pieces?
OVERVIEW You can colour each part of the rifle without separating it as a whole. To texture a mesh a popular way is to unwrap it on a UV then then colour that UV in which is your rifle flat down when colouring it in you can change the colour so blue for the grip and red for the tip etc all at once no need to seperate the mesh.
First you need to unwrap it, you can do this in edit mode by pressing u and selecting smart UV unwrap then from the 3D veiw you can go to UV/image editor while the rifle is selected you will see rifle flat if its all bunched/overlapped then you will have to unwrap it yourself just make seems with crtl-e then select unwrap the seems will separate it and stop it from being overlapped.
Now you have your rifle unwrapped you need to place it on something so at the bottom click new and click ok this will place the unwrapped rifle on a UV. You can then add colour to it by selecting paint from the UV mode (it would say "view" at the bottom).
Once in paint change the colour in the tool bar on the left and click on the UV to paint on it, you will see colour on your rifle in 3D view once you change your view port shading from solid to texture (the UV is a texture applied to the rifle).
I highly recommend you search on Youtube how to texture there are heaps of tutorials that will teach you in 5mins but I also wrote it down here.