20g long planted.

java fern and anubia grow fairly slow and do not require much of a "bio load" those lights are fine, my 65g is full of monster size anubia and java fern they are bullet proof!

do not bury the anubia rizome tie them to logs or rocks. same goes with the java fern, java moss would be a nice touch as well.

Most low light plants will be fine with that lighting. Depending on your stock, you would probably ok with the nutrients produced (you can always target dose if needed) or add one of the broad spec ferts, like Flourish comp. Some plants are heavier root feeders...Cryptocorynes and swords, for example, sometimes do better with root tabs.

I'll never go back to plastic plants again. Live plants are so much better.

I prefer peacock moss to java moss, because I think it's prettier, but it's harder to find. I probably should take pictures of the huge masses of peacock moss I now have in my tank.

A red or brown wendti crypt would give a different color, most crypts would work in that light. Crypt. parva is quite small. jpappy is right, they do like root tabs. You could try some spiral vallisneria, mine's little out of control with spreading in a 20g long, but I'm lazy. A nitrate level of 10-20ppm is a good range to aim for whether from fish food/poo or from ferts. I'm not a huge moss fan, it can catch & hold detritus. Shrimp can help groom plants but IME don't really control algae. They also don't eat much so don't really add a lot of bioload. I'm into "nano fish" in small tanks. I have rosy loaches & CPDs (formerly galaxy rasboras) in mine. There are several small rasbora & rainbow species & dwarf corys are fun. All could be kept with shrimp, cherries are easy.

Start with a few plants and a few fish then work your way up as you get a feel for it. There is no definite answer as it depends on a variety of factors including your filtration, fish eating habits (how much falls to the bottom), lighting, etc. You can always dose KNO3 to supplement nitrate if needed, but again if you start with a school of 10 tetras and a few plants there should be no shortage of nitrate. That isn't to say you won't run into other nutrient deficiencies, again it all depends.