cardinal tetras

I just started a 3 gallon aquarium. It is a cheapo from Walmart. the Aqua 360 that has an aerator bottom gravel filtration system. (I know it really doesn't filter anything). I purchased some gravel, 3 plastic plants tall and 2 mediums, and a translucent plastic jelly sea amenity. So I went...

I just got a Zebra Loach and 2 Clown loaches and 3 cardinal tetras a couple days ago. And one other fish but I forget the name. I was wondering if I should get another zebra loach so he won't be the only one in there. Also I was wondering if I should get some sort of cave that the zebra loach...