For a 55, you might do well with the discus, the cardinals, the corys and either a bushynose pleco or a couple malaysian trumpet snails. Those snails don't get too big, they play in the substrate and stir it up for you and their shells are too hard for discus to eat. Oh and they don't mind the higher temps. I had one in my tank in the beginning and now have 10 that I can count. It only takes one to breed, so don't buy too many or you'll be overrun with snails..lol
I'd leave out the rasbora's for now and maybe add them later once you've had time to figure out if they will fit into the tank once the discus start to grow. And definitely nix the chinese algae eaters.
If you really want to grow out the discus, get 2 forms of filtration (trust me, if one fails you're going to be glad you have the other one!). I have a hydro sponge filter and a canister filter, but a hang on back filter is good too. The hydro sponge will do a good job for the bio load, provides some mechanical filtration and also helps add oxygen to the water, which you need at the higher temps.
Other things you need.
2 heaters so that the stress of the higher temp isn't too much for one heater.
A good variety of high quality food so that they grow out into nice healthy fish. Discus flakes, pellets, frozen beefheart recipes, frozen brine shrimp cubes and freeze dried blackworms are all good choices. Just get the ones that you like best.
If you really want a planted tank for the grow out, be sure to get super easy care plants because they are going to be subjected to water changes every day and will get abused by your syphon. The other option is to put a couple pieces of driftwood into the tank and tie anubias onto that, so you get the look of plants and can just lift them out while you vacuum.
Seriously consider the advice given above about having a bare bottom tank for ease of cleaning. I am super diligent with my 4" discus and it's still a big pain to vacuum the gravel and plants every single day. And 4" is WAY less work than the little juvies.
Some people put a very small amount of sand on the bottom so that it gives the illusion of substrate. That might be an option for you.