The Orange crayfish are cheap on aquabid if you are interested. Of course they may eat plants, they may not, research it...
Dwarf gouramis shouldn't be kept with each other besides male and female. They will fight for territory. They are like bettas but can take a bit more current. Females are almost never sold in petstores because they aren't colorful, so less sales.
You could get the same effect as crayfish with ghostshrimp and they are cheaper. They are just see through, it is really cool looking, and they won't eat plants or fish, besides dead fish or other dead shrimp. Just don't let them near babies, they may eat them as they are small. Easy to take care of as well, they will eat fallen betta pellets and sinking cat fish waffers that are meaty.
15 Gallon NPT
1g no tech bowl in the making