To help with your questions, like the previous poster stated, the scraper bar on the machine can be set to litterally scrape the driveway by adjusting the skid shoes on the sides of the bucket. I have mine set to leave about 1/8" or so, and while at times it may freeze up under right conditions more often than not by the next day or 2 I also have mostly clean driveway due to the sun. The shoes can be lowered all the way down to give a clean driveway all the time but this will wear down the scraper (a part which you can easily replace) after a few seasons I would say.
As far as storage the handles can fold up a bit on the compact models, they fold forward toward the engine. Floor space will be similar to a normal push behind mower (specs can be found online). The difference is the height as the chute and engine height are obviously higher than a lawnmower. I suppose you could take off the chute for summer storage and fold up the handles to make the machine as small as possible but for most people I don't think height will be much of an issue as floor space. Again I won't bother folding the handles on mine because you can easily slide a mower or something else on the shorter side right in behind it and the handles are up high enough to not really cut into much storage space.
FYI I just did a quick measure for you, floor space is about 3' length from the front of the bumper to the point in which the handles fold. Width is about 24" (22" bucket plus a skid show on either side) at it's widest. Folding the handles will save you about 18" overall length, as the machine exceeds 50" from tip of bucket to tip of handles, but again this extra length is at about waist height and you can fit something behind it if space was at a premium. Height of the machine to the top of the chute is also about 3' but taking it off doesn't seem worth the trouble as it would only save you maybe 6" tops until the height of the engine comes into play. This was based on a quick measure of my subaru powered compact 22, the briggs powered machine may vary slightly on engine size and height, but I doubt it would be that significant.