African Dwarf Frog and Eclipse System Three

Just curious if anybody can help me out.  I bought an Eclipse System
Three (3 gallon) filtered aquarium and an African Dwarf Frog.  Right
now I have a plastic plant and a small clay flowerpot for her to hang
out in.  I feed her frozen brine shrimp and she spends hours jabbing
her snout into the rocks hunting.  Then just relaxes in her cave.

Anyways, I used smooth medium sized (1/4" - 1/2") epoxy coated gravel.
 Everything I read about these things says not to use anything sharp
or small for the substrate.  They might hurt themseleves or eat eat
it.  I also covered the intake with some cheesecloth so an arm or leg
wouldn't get stuck.

I was orginally thinking about adding a betta.  I have one right now
in another 1 gallon aquarium but would buy another.  But I have heard
that it is possible that they might not get along too well.

If I don't add the betta, would it be too small to add another frog. 
I was also considering adding a couple of ghost shrimp.  I am assuming
they pose no threat.

Does anybody else here have any other ideas what I could add without
overcrowding the tank?

I also would appreciate any ideas for a live plant.

Thanks