You're not going to be able to do a heroic at <80 - the whole point of heroics is they're designed for well geared max-level players. All the mobs will be level 80 and bosses will be 82-83.

Personally I haven't had any issues questing really. Theres only one instance you can do right off the bat at level 70, utgarde keep - about 10 seconds of reading one of the 90 kojillion websites covering the wrath launch would have told you this. Also how do you not know how heroics work if you have a full team of level 70s??