are far as water changes i cycled my 75g out with 40lbs of live rock and experienced little to no cycle time at all, i made the mistake of adding my 2 baby O clowns too early so i got some bio-spira and it helped calm my tank down. make sure you test everything everyday and try to do it at the same time of day; in the morning when the light goes on, in the evening, then when the lights go off. once your tank has settled down wait a week or more to make sure your tank is ready to handle livestock. As far as water changes go i do it according to my trates and the level their at... but typical i do a 12g water change a week.
as for your second question i hear distilled water is better then RO
but it depends on where you get the distilled water from, i guess some use copper pipes and if you dont know by now copper is not good for reef tanks. and for that last question im not sure if im reading it right but for your top-off you dont want to add salt to this, but for your water change you want the water to have the same SG
and temp before you add it to your tank. i use a spare pump and heater in a bucket to accomplish this.