I have 6 discus, a krib, 2 bolivian rams, tetras, clown loaches, and rainbowfish in a 125. My Bolivian rams are territorial but not towards fish bigger than them, Once my keyhole outgrew the ram, he stopped getting bossed around. My discus run the tank, they don't let the rams get near their food. My krib who is more bossy than aggressive doesn't even go near my discus.
When you buy discus, you want to buy the more sociable ones, the ones that come to front of tank when you approach. IMO, I would say get the discus first, maybe up to 6 and then gradually add the other fish that you want. If they aren't compatible, take them out and replace them with a different fish. Everyone will have different experiences so you'll have to use trial and error and proper judgement to see what works for you. If I asked if I put the fish I got in my tank "online experts" would yell NO, but I've had this setup for almost a year with few problems.
When you buy discus, you want to buy the more sociable ones, the ones that come to front of tank when you approach. IMO, I would say get the discus first, maybe up to 6 and then gradually add the other fish that you want. If they aren't compatible, take them out and replace them with a different fish. Everyone will have different experiences so you'll have to use trial and error and proper judgement to see what works for you. If I asked if I put the fish I got in my tank "online experts" would yell NO, but I've had this setup for almost a year with few problems.