If this is your first time owning fish then I suggest you go with the Lemon Tetras in a shoal of 8 or 10 and Replace the Dwarf Gouramis witha Gold, Blue, or Opaline Gourami. These suggestions are more hardy and good for a first time aquarist. Wait a few weeks before you get a Pleco.
If you have owned fish before then get the shoal of Lemon Tetras and your Gouramis. Do not mix Tiger Barbs in with the Tetras and Gouramis.