82 might be a bit cool for Discus. I would bump it up to 84. I have a planted tank with swords, ferns, etc. and they do just fine at that temperature.
The pH is a non-issue as long as it's stable.
Loaches are a social fish and do better in groups just like Discus. They are also almost always wild-caught which means that a strict quarantine of at least 6 weeks should be mandatory before introducing Discus. Preventative treatments on your loaches for parasites and bacteria would also not be a bad idea.
Also, do you intend to buy adults for your planted tank? You are setting yourself up for problems if you are intending to grow out juveniles in that environment.
JMHO
-Ryan