Hi Dave, welcome to fishlore!

Your tank is gorgeous... just the way it is! BUT I sure understand wanting to change things around some...

Your choice of fish sound great. Discus and rainbows and GBRs and Angel fish are all great fish.. But you have to take into consideration the water temperature of each species. The rainbows prefer a cooler water temp than say the Discus. Angel fish can do ok with the Discus at the higher temps but not the rainbow fish or neons. But Cardinal tetras can do fine in the higher temps as can the GBR.Not sure that the cories would do well at the higher temp either.
So If you wanted Discus, Id say try the GBRs, cardinal tetras and angelfish.
If you didnt want to go with the Discus, you can do the angelfish, neon or cardinal tetras, cories and the boeseman or any of the Australian rainbows for that matter, there are so many beautiful ones to choose from.
Discus really need a lot of TLC, such as frequent water changes and those higher temps. I think you would have more of a choice of fish if you omitted the Discus's needs. ahhh so many decisions lol... but so much fun!
Anyway.... glad to have you on board!

~ kate