I can't answer all of your questions, but I had a similar experience with cardamine. I bought it on a whim, and the leaves started yellowing and the new growth was smaller. I read someplace that the plant is not ideally suited to tropical tanks - I can't remember now, but maybe it was temperature(too high) that was the issue. Amazingly, I still have some stems of it, but it has very small leaves. My tank was gravel at the time I got this, with excel dosing and flourish, with high light.
If you like the look of the cardamine, it might suit you to get some pennywort. It really does look the same, and grows really well in my tropical tanks.
Also, I have no idea what a lily pipe is, so sorry to not be able to help.
1 - 55 gallon planted community
3 - 10 to 20 gallon planted betta tanks
My advice: slow down, think, and be willing to learn. Then you'll be fine, no matter what.