for 1 and 2 when i say balance, i mean the levels of each instrument. for your last paragraph i mean not in the fatiguing way. i mean if any is too pronounced, when you master, that frequency will be the first to rip or clip. so if the mix is balanced, then one can jack it up to a good level, adding gain and compression and eq gradually w/o a particular frequency sticking out. Two differently mixed and tracked songs, with good balance among the levels will both have a better chance of getting subjectively "good levels". That's why the kastigo album is one of the loudest ive ever done, hazel's mix was balanced and jacking it up was a breeze. i could still make it louder, pero prumeno na muna ako before we get too crazy with the levels. if the guitars were too piercing, or the vocals to loud, or even the kick too spiked, there will always be a disadvantage, where "leveling" is concerned. but again that's not always a bad thing. louder is not always better ika nga.