Also, my substrate is gravel and I don't think I'm ready to tackle sand or soil just yet.
So far in my research I'm considering Anacharis tied to the gravel, Water Sprite floating, and Java Moss on some of my decor.
tied
For now, with plain gravel, I'd suggest staying away from plants you root into the substrate. Since you'll be moving everything to a larger tank, convenience would be a good way to go with plants.
I think there may be some better choices for you other than anacharis. This plant sheds leaves rather easily making a mess on the bottom of the aquarium. Also, I am told, if you plant it, when it reaches the surface, it flowers then sheds all of its leaves at once. You have to be sure to keep it trimmed up.
The best plant type to meet your requirements would be any of the Anubias varieties. They are low light, very hardy, low maintenance plants. The best part is you tie these to driftwood or rocks, so they will be easy to move.
Another plant category to consider would be java fern. Also very hardy, low light, low maintenance plants that come in various shapes and sizes as well. You also tie these to rocks or driftwood.
Other floating plants to consider would be Wisteria, Frogbit, and Duckweed. All will be easy to transfer to another tank and are about as drop in and forget as it gets with plants. I have all three floating in my 5 gallon and I just love them. With Duckweed, though, once you have it, you'll likely have it for life. It grows in thick and sticks to everything. To keep it from over running your tank too quickly, use it with Frogbit (it inhibits the growth of Duckweed).
