Boof head,
It may sound a little unhelpful and unkind, but answers to questions like these are very hard to quantify, and answer in a single message. This is years of experience type stuff. You're sort of asking "how long is a piece of string, which is in a box, supported by an uncertain surface". There are many things to be aware of in this type of operation, which you really only learn by doing them many times, in the company of a really experienced pilot.
Personally, I would not be landing a Beaver onto 20cm of ice, unless I knew that ice very well from recent personal inspection.
The safe amount of space for the types of manuevering you mention is very much determined by the pilot, and his sense of personal skill. It's kind of like buying a Rolls Royce; if you have to ask, you can't do it.
Seen from a different perspective, I wouldn't think to tell a pilot how to do the things you mention, then expect him to go out and do them safely. Landing on any snow has may hazards, unbroken snow, and snow covered ice just add to the hazards. Doing it with any confinement because of topography really complicates it.
There are so many things to be considered for any off airport operations, which are all best done based upon actual experience, not ground school.
There is a lot written about winter bush flying in Canada. Start searching some of the famous bush pilots, and the stores will come to light for you..
I hope that it is helpful to say that training this sort of flying is best left to people who are really familiar, based upon actual experience.
Good luck, Pilot DAR