Will winners have a choice of prizes or are they are awarded randomly?
The prizes will be drawn randomly.
What are the options when someone wins a prize (like a dojo membership) that they cannot or do not want to use? Can people arrange a prize exchange with another winner or otherwise transfer such prizes?
Such exchanges would be perfectly fine as would the winner's presenting the prize as a gift to someone else. The exchanges and such would be done personally (ie on their own).
Hope that helps clarify,