So here is some advice.
Tip 1: Don't run 24/7 mode. Cut it back to lets say 50% unless you are putting the light on stilts. I generally run around 5-6 white, 5-6 blue, 3 green, 6-7 red. Guessing a bit with the numbers as its been a while since I last set it. Blue and red promote most of the photosynthesis, while white and green are largely for aesthetics. If you raise the light up, 24/7 mode is possible, but I would estimate 12-18 inches above the tank (Purely a guess as I haven't implemented it, but raising the light reduces its penetrating power.).
Tip 2: Even if you don't like or want them, run some FAST growing stems at the start like wisteria. When you first set up a planted tank, everything is almost guaranteed to be out of balance and you will have an algae nightmare on your hands. When your plants finally start to grow in and you have a dense scape, start removing some of the unwanted stems.
Tip 3: If you are running open top or there is some decent space between the lid and the waterline, consider adding some floating plants. This is the same premise as the wisteria, plus it provides some shade. With modification to water flow, you can direct them over your lower light section.
Tip 4: A light layer of super glue will work for attaching plants/moss. But the bigger the amount, the more it will show. Superglue dries white in the tank, and can take a couple months to grow over and hide. Thread, fishing line, or rubber bands can also be used to attach plants. Thread will eventually dissolve and you can match need the color of the scape to hide it. Depending on the fishing line material, I believe the line and rubber bands degrade after a longer time.
Tip 5: Attaching thin amounts of moss over a wider surface area is better than thick clumps. This allows the rooting pieces to attach easier, as they are receiving more light and are the portion that has to grow. If you attach too much, the tops will grow more and the moss may not root.
Tip 6: Use super glue that is a gel form as it doesn't run everywhere and make a mess. The form that contains cyanoacrylate is the correct type. IF THE GLUE DOES NOT SAY THAT ON THE BOTTLE OR PACKAGING DO NOT USE IT.
Tip 7: Not really a tip, but I would research the exact plants you plan on growing. Some grow better in different forms. For instance, plant x may not look full in substrate A, while plant y may not be able to root effectively... For the most part, I use amano soil (very light and a pain in the ass to get some plants to stay down in plus messy to rescape), dirt (you don't want, but messy to rescape), BDBS with root tabs (depending on the tank one of my favorites as its fairly heavy and not bad to plant or rescape). I have as used flourite and hated it, but not real a fan of the gravel look either.
Tip 8: CO2... GLA makes some of the best regs, but they are $$$. Others can be found cheaper, but I have never looked into them. Always buy the largest tank you can fit, as the cost of refills aren't that different. This is NOT real pricing, but lets say a 5lb bottle is $8 to refill, while a 10 is $10, and a 20 is $13.
Tip 9: Another CO2 one, kind of. Make sure you have sufficient circulations. A 20 long can have several dead spots. This is bad for multiple reasons like waste buildup. But with CO2, one side of your tank may flourish while the other suffers. With a singular light spanning the tank, both sides are getting the same amount of light, while one side may be CO2 starved.
Lastly, non green plants. I have always preferred crypts, but they aren't short enough. You could try AR mini. Lots of people have luck, but they just don't grow for me. With serious trimming, you could probable get a ludwigia species to be short and bushy. Then main problem I see here is these plants probably need to be under 4-5 inches and maybe less. If you want color, I would suggest counter balancing the tree with some stems on the opposite side of the scape. Even a 8-12 inch stem is pretty short, and you could do something like a "forest of stems" on one side, followed by an open field of grass, and a lone tree in then field. The benefit to this is you have a second hiding place for the fish (if you add them) and a place for shrimp fry to hide. This will help them feel more secure and the can feel comfortable swimming from one side to the other.
HOLY TEXT BLOCK...hope this helps.
