Well pics you posted are not really what you would call a discus biotope, I’d suggest you do a google search for “discus biotope aquarium” and see how they differ from the Japanese style aquascapes in your pics. Also color spectrum and intensity in those photo are not really representative of aquatic plant tanks, those are just under low level morning/late afternoon viewing only lights. Be very hard to grow most plants under that lighting. Most the lighting in fresh tanks will usually center around using 6500k whites as main lights and supplement those 660nm reds along with blues. Not sure on your light but it may use 10000k white, not that plants can’t adapt to use most spectrum it may not give appearance that you like.
That said, as noted above, there are many hybrid approaches to fresh tanks many have implemented successful.
Main things you will need to learn.
1. Circulation and turnover in tank and biofilter. Be prepared to reduce flow in your tank by probably at least 40% compared to a properly set up reef. These are much quieter, calmer waters overall. Protein skimmers don’t work in fresh. And your losing the big wall of biorock that is base of most reef setups and may need to rework sump to compensate, but that can depend on fish and plant load in tank.
2. Chemistry. You can probably throw out 90% of what you think you know about water chemistry now that your going to lower PH/KH/GH. Two examples, ammonia is no longer as super toxic as before and your target for phosphate is no longer 0, .5-2ppm phosphate is normal.
3. Don’t get caught up in a lot of super high dosing, high tech rollercoaster thinking that’s what you need. Unlike reef which has pretty stringent requirements to be successful there are all different .shades of grey.
I myself wouldn’t pick those two types of setups as tanks for cardinals or discus, that’s not type of environment they require. As posted above discus can be a picky lot.
If you want super simple low maintenance something like this would be easy, easy way to go. Roots for fish to feels safe in, super easy floating overhead plants providing the dim lighting they prefer. The floating plants access all co2 and light they want and are one of best water cleaning filters you can get. Only plant maintenance you have to pull is snipping out a bit of floater and tossing them to keep numbers and light diffusion in tank how you like it. Do that, change 25-30 water weekly, clean filters and your done for cardinal oriented tank. Discus will require more frequent water changes.
Add 48 cardinal, a herd of cory cat rooting around on bottom sand cleaning up excess food, maybe 2 dozen lemon tetra and you’ll find the calming aspect of a backwater/forest type setup is so relaxing to just sit and watch, complete opposite end of spectrum from hustle and bustle of most reef setup. The dimmer slightly diffuse light of overhead plants will just make cardinals blue sparkle like glitter in tank. You can add a few spots of sword plants or others to mix it up bit. But great thing is you barely have to lift a finger to keep tank running once you get plant load, fish load, filtration and a few water changes/routine dialed in.