Add 1.03 only.
Mods will be stated as GWX compatible. However, try GWX before you add a load of mods, you may find you don't need them. GWX also installs JSGME & a set of GWX Authorised mods, you'll find them in the installation folder.
Any skin that uses textures only is compatible with GWX. DO NOT use any skins that are packed into DAT files unless the readme/release thread says that they are GWX ready.