I got a 2 stage Sears Craftsman 5 HP 22". It's a 1986 model, I know it's old. I can lift it myself, but it is heavy, and I'd rather use ramps. No matter how deep the snow is, or how wet, it throws snow far.
Figure it this way, you can get an 8 HP 24"+, that you NEED ramps to load, or a smaller 5 HP 2 stage, a little narrower, and a lot lighter. Not as light as the 2 stroke models, but it is worth the added weight.
If you use a 2 stage 8 HP, 24", you typically go down a sidewalk, and then come back down the walk clearing another 1/2 width or thereabouts. Most walks are about 36" wide. If you go down it clearing a path, on your way back, you naturally open it the full 36" width.
If you use a 5 HP 22", you do the same thing, and can still open it the full 36" width.
I wouldn't get any smaller than a 5 HP 2 stage blower. I have an Ariens 8 HP 24", but I keep it as a back up. WIth that machine you NEED ramps. It's REALLY heavy compared to the 5 HP 22". Keep in mind I do mostly walks along the curb, that get covered by what the road plows toss up. I don't think the small single stage blowers can handle the wet, often frozen snow the road plows toss up. Doing the walk up to someone's door from the driveway, yes, they can. But consider that you may have to turn down work, if all you have is a single stage blower.
I myself have gotten calls after heavier snowfalls from businesses that want their curbside walks cleared. These are the type of places that the store owners do the walks themselves. That is, until we get 14" they don't feel like shoveling the morning after. With a 2 stage, you can go there and clear the walks in a matter of minutes. With a single stage, it will take MUCH longer, or you may have to pass on the job all together.
Like Geoff said, he has the single stage, and 2 stage blowers. If I had to buy one to start out, I'd get a 2 stage, and get a single stage later on, but that's me.
That way I'd know I have a good blower that can handle anything. Keep in mind todays blowers are larger than the older ones. By that I mean you may find 5 HP models that are 24" wide, and much taller than the older models.
You may just want to get a good used blower from a homeowner. Often all those machines need is a new carb, from sitting so much with fuel in them.
~Chuck