Kuhli loach and sand in my aquarium?

Two things I am planning on saving for... unless I learn that I shouldn't. I have a biocube 8 with, so far, a little fish which I do not know what it is called (looks like a tetra, kind of like a rummynose, but no red, and just one black mark on tail) with a peppered cory catfish. I have gravel that is probably the size of two peas put together for each rock/pebble. I was planning on getting maybe white playsand, and a kuhli loach? Would this work in my aquarium? Is there a better kind of sand I could get? Pros and cons for the sand? Should I get a kuhli loach?