As John stated, as long as there are no large particles in the dirt, it should be fine. Things like bark, moss, and gravel could cause impaction. If you want to help prevent ingestion of substrate, use a feeding dish. I just use the lid from my worm container.

Sexing should not be based on color of the frog. Both sexes will develop yellow color where appendages meet the body. Males can have more yellow on the sides and stomach but this is not the best way to tell. In males, a large head to body ratio is a good indicator. Post some pics and we can give you our best guess.

If you stick your finger in front of a pyxie, it will most likely strike...they are aggressive eater. Come at the pyxie from behind and "scoop" it up rather than grabbing at it's back/legs which might seem like a predator.

Do you pick your frog up to place it in the water bowl? If so, this is not necessary. As long as the bowl can be entered/exited easily, the frog should go in on it's own. It you keep humidity up then the frog will get a lot of moisture from the substrate. If you notice the frog never goes into the water, a weekly soak might be a good idea to help it poop.

What is off putting about a male pyxie? They're awesome and actually the more desired of the two sexes.