Hi and welcome to the forum Ally.
It seems to me that the solution for the most issues you have addressed in your initial post would be to just buy half to fully grown 5-6 inch discus .
That way you can have a nice and fully set up community tank for your living room and a happy hubby on top of it , right from the start
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If you do decide to grow young discus then a couple of driftwoods with attached plants in a Barebottom wouldn't hurt the water quality if you do your regular maintenance and Waterchanges .
Chlorine / Chloramines can be addressed with just adding Dechlorinator during WCs , so no real need for RO unit just to combat tap water chlorine.
Discus are very friendly fish that always swim on the front glass . Although they have their own pecking order and pairing behaviour that is interesting to observe , I'm afraid everytime you approach the tank they will beg for food on the front glass no matter how well fed they are , just like your goldfish .
And lastly I wouldn't recommend any other fish in their growth phase .You can add food competitors and other species once they get half to fully grown or at least 5 inch size .
Good luck with your decisions Ally and I hope you will be able to make your koi Pond dream come true some day .