My workflow is: applying the solidify modifier BEFORE unwrapping as it changes the mesh. If I used a mirror modifier I first set the seams (I usually do manual uv unwrapping), look if it's unwrapping is ok and then apply the modifier because this way I've already set the seams and do not need to do it for the mirrored side. For the subdivision: I always do the unwrapping BEFORE applying the modifier to be exact I almost never apply the subdivision modifier. This way it's eathier to change the mesh for further modeling. You can export your model as object and tick "apply modifiers" in the export obj options tab, you do not need to apply modifiers before exporting.