I made these ones :)
You may go on with a no filter aquarium if you don’t plan to have fishes, and you already know how to keep it healthy like that. The plant you are looking for must be Hydrocotyle tripartita japan — just google it to check. It is a hardy plant that could thrive in less than ideal circumstances, too. As to the number of shrimps — they regulate their population quite well — I’d start with easy ones, such as Red Cherry Shrimps — especially in a tank without filtration. Start with 10 and you’ll see their population growing until they don’t decide not to reproduce anymore — they’ll know what is the right number for them. The only thing is that they need fairly hard water. The same is true for all kinds of shrimp (population-wise), but the more expensive ones usually require soft water and well regulated temperatures. I hope this helps — and good luck!!