Your bump map is set up correctly. If you want to use a subsurface color, you need to give the subsurface a vale that is higher than 0 (although low values generally work best). If your .png image has built in alpha channel, you can do it all in one material. You can connect it like this:

[![ShaderCombo][1]][1]


  [1]: https://i.sstatic.net/oTPMe.png