here is the link to the lime wash thread (there is an old (1930th) booklet on the directions/technique

http://www.truefresco.com/dcforum/DCForumID1/92.html

good luck

PS. As of sealing drywall mud I do not see why it would be needed, however the best solution is to test:

limewash a small section and see if it works for you,
if not seal it with latex paint