Plants usually involve a little bit of maintenance…thinning them out when they spread, removing yellowing leaves, keeping bits out of your filter, etc. I love heavily planted underwater jungles and tend to lean to the easy plants (no CO2, can grow in gravel substrate, floating/fast growers). You seem to be starting that way also.
With a 55 gallon tank the height is probably somewhere around 20-24” so you could grow a very nice amazon sword plant. Here is a picture of a huge sword plant in my 46 gallon bow front tank, way back in 2007. You can see I believe in a large variety of food for my fish, and you’re not even seeing the fish food in my freezer, LOL. But anyhow, the sword will send off runners with more “baby” plants and once they grow a little you can plant them too. You want to leave the crown just above the substrate (don’t pile the gravel all the way up to the green stalks, leave some of the beginning of the roots above the gravel line where it connects to the green stalks - I guess you can kind of see that in the photo too).
Since you have some floating plants and plants that can grow attached to rocks/wood, I would suggest you get a good copper free liquid plant fertilizer (shrimp safe). For the swords though, I used a root tab and once every few months or so I’d push one down in to the gravel near the base of my swords. Just be mindful when you vacuum the gravel not to suck up your root tab.
If you keep angelfish in your 55 gallon, they may lay eggs on the sword plant leaves. If you breed angels though, you don’t want any other fish in there with them (and usually a 20 gallon tank is used for a breeding pair anyhow).
Susswassertang is a one-cell thick algae which shrimp love to hang out on and if you wrap some onto a nice round rock (use some cotton thread to wrap and hold the susswassertang to the rock) that can grow into a nice little round bush in your aquarium. Do a search to see what I’m talking about and research more on that plant to see if you would like that. I have that in my crustacean tank, along with many other plants too. It is very easy to grow, it is slow growing.
Another one you might enjoy is hornwort. It is much faster growing, especially with good lighting. It becomes quite bushy and can get to be 10 feet long or more. So you do have to trim it. You can share your extra with other aquarists, trade some for new plants, or toss it in your garden/trash bin.
You should show us a picture of what you have. What kind of aquarium scene are you hoping to achieve?