I used to have a Kawasaki motorcycle. We had similar issues when you put a bike away for the winter.
On leaving fuel tank full of fuel,
Tanks are made of metal. As mositure gets inside in an empty tank it slowly corrodes it. Thus the logic is if you fill your tank with gasoline which of course doesn't mix with water, thus displacing water, the end result is no corrosion during winter. So the advice was to fill fuel tank all the way to the top. Of course, using Stabil and similar fuel stabilizer is a must. Goes without saying.
My snowbloader and push mower both have plastic tanks, so corrosion is not an issue. Thus I drain those machines. For cars I fillup.
As for oil,
Again motorcycle riders would put in new fresh oil in the fall to get the contamination from summer riding season out. Clear enoug. Now some/many would dump that oil in the spring before starting a new season. I asked them all why, what is point. The only feeble excuse was that during winter moisture gets into oil. Certainly oil cannot degrade for 6 months in an idle engine.
Everyone here says that moisture burns off from a decent longer ride that gets engine up to operating temperature. Certainly air cooled engines like snow blowers have no problems warming ip
So if you first snow blower run is of a decent duration and burns off any mositure that might have gotten in during summer, then the oil should be as good as when it was put into engine 6 months ago, right?
In other words, it is a waste to dump "storage oil"
That being said, sometimes, such as my summer car, I may put in a cheap weak oil for winter storage. Then in the spring I'll just use a shorter OCI. That is kind of a compromise as I do get some use out of the storage oil.
BTW, most advice here is great. Good stuff