Theres really a ton of misinformation you have received. Ignorance runs wild on social media.
I think you will be fine. You sound well experienced and the fact that you are questioning what you are being told is a good sign.
The hero fish is your best chance of detecting a problem but a well cycled sponge from your established tank and some tank water will be a good subsitute given you can't do a hero fish.
You can mix stock from suppliers after a lengthy QT... I would suggest 6-8 weeks. It is easier to get all discus from same source at same time ..but most people dont for various reasons. Theres always a chance fish will crash when.mixed...but a long quarantine goes a long way to preventing that.
absolutely not but more countries are breeding them and shipping globally. Different water means different organisms,bacterias and virus. Theres also a greater chance of pathogenic bacteria that are harder to treat as antibiotics in aquaculture is a huge problem.Have discus really developed into such weak and zero immunity animals over the past 15 years?
false.I've been told, that I need to keep albino domestic discus only as non-albinos will turn black or pepper in a planted tank)