As for the length, I will add my 2 cents.
Kal calls for 50' (1/2 OD ss coil) in a 20 gal blichman. I went with 25' in a 15gal keggle. I didn't like having too much coil where the coils touch each other and there is twice as much liquid working against the target HLT temp. In my setup, there is about 1.25" of space between the coils so the hot water will actually have an easier time of affecting the temp inside the coils...at least that is what I expect...still building.
If that made no sense, let me know.
And now you see that Evil will always triumph, because Good is dumb!