If it was designed to take normal tuning and thats how you like it then use that tuning. If you unnecessarily tune lower, the intonation will be comprised (This isnt necessarily bad, after all we use plenty of different tunings on guitars all the time...). if you are unsure I would look up the model or write to Ibanez. I would imagine some of the heaviness might come from extra reinforcement. It is usually older models that are designed to be tuned a tone or two lower. I would imagine an Ibanez is intended to be tuned at concert pitch - although check with them!
String 12 string - I string in pairs and work from the middle out - D, G, A, B, low E, top E.
Also check which octave comes first. On most 12 strings, the high octave precedes the low octave. On a few models this is reversed.