Much of the decision on what is the minimum depends on the area to be cruised. I suggest that cruising in tropical areas in a 26 foot boat is not the same as cruising in Alaska in the same boat. In areas where most of your time can be spent on deck, a smaller boat may be more than adequate but if your cruising goals are more northern wilderness than tropical harbours, being able to get inside becomes pretty important.
Similarly, cruising in high lats lessens or eliminates the need for refrigeration.
There is a tide in the affairs of men,
Which, taken at the flood, leads on to fortune;
Omitted, all the voyage of their life
Is bound in shallows and in miseries.
Shakespeare, Julius Caesar IV, iii, 217