HI bs,
Top dress as soon as possible as this way the lawn will shoot up through it opposed to it being smothered and having to struggle through it. basically you're putting soil on top of soil with roots in it.
I always use nothing more than orange Brickies Sand (the darker orange the better) and never all these expensive "concoctions of whatever". I will be using it again this year and I spread it out on the warn concrete and totally dry it out, this way it will run in to all the low spots just like the sand goes through the hour glass when you screed it around.
As far as using the Scotty is concerned just ensure that your bare exposed soil is just a tad damp so that it doesn't stick to the rollers and not too dry so that the air movement created by the reel doesn't flick it up like a rotary would do. No need to use the rotary for anything else other than the scalping process. In other words you could store the rotary totally off site as that's how much you're going to need it.
Cheers,
BB.
