Good advice previously, I've a couple of follow-ups.
The "sand" such as a plant substrate is a bit different from "play sand" so you should not have any issues provided there are live plants growing (their roots in the substrate work with the bacteria, etc). And this "sand" will be fine for corys or loaches.
But not the clown loach. Not in a 25g tank. Clowns attain 12+ inches and if you read our profile on this fish (click on the shade name, or use the second tab from the left in the blue bar across the top) you will see the minimum size tank required, and they must be in a group of 5-6.
And while undergravel filters can work with planted tank, they will not work with sand, and they are not the preferred filter. In a 25g a simple sponge filter is adequate. The forest fish do not like excessive water movement, nor do the plants [the reason is explained in Part 3 of the series "A Basic Approach to the Natural Planted Aquarium" stickied at the top of the Aquarium Plants section]. I only use sponge filters in tanks under 55g.
As for SA plants, most of the species in our plant profiles so far are SA, so have a look at those. Under "Tropical Fish Profiles" in the blue bar.