If you buy a few and get things right, everything will be good and you will eventually have more plants than you know what to do with. However, should you buy a tank full of plants and get it wrong, you are going to end up with a tank full of dead plants. I bought a few vals and compact swords for my 75, and things were fine at first. The vals were sending out runners and multiplying and the swords grew decently tall and full. Then, everything stopped and they started dying. After a lot of reading, I figured out that I needed ferts and CO2 with that amount of plants in the tank. After an algae bloom or two from the ferts, I eventually got everything under control. Then, I switched from Flourish to dry ferts, and it took another 2 algae blooms to figure out what I was doing wrong. You will always be learning.
Did a water test yesterday and found out that I have 0 nitrate. That had never been a problem before with the 14 loaches and 8 plecos I have in the tank, but it would also make sense since the plants aren't growing quite as quickly right now. So, now I might actually have to start doing nitrate. Never thought that would be the case.