Kuhli loaches are best in shoals of 5-6 or more, but grow quite large, so I'd say that youre best off without them. For a shoal that size you need at least 50 gallons. I'd swap them out for a shoal of 6 or so corydas catfish.
Guppies or tetras (depending on type) would fair well in that tank. Depends if you want something that may shoal or not. The tetras will shoal, so keep that in mind when determining how many you are getting.
You could also get another DG or two, provided there are sufficient hiding spots in your tank.