I almost always use 6 lines in situation A or B and 4 lines in C. I'm a big believer in spring lines, and usually put out two. I carry 6 lines, each the length of the boat, all 5/8" braid. That's usually more length than I need, but I would rather have 10' too much than 1' too little.
We also carry a set of 3/4" storm lines.
I do admit that I'm something of a rope junkie.