First, nice character idea, sounds like it would be a blast to play. As far as I know, though, there are no 4e guidelines for creating a path. However, I have seen similar questions on AEG's forum for l5r, so I bet taking a look or asking there would be worthwhile.
http://www.alderac.com/forum/viewforum.php?f=250

As for my 2 cents, I'd say that travelling among the dojos of various clans and getting sensei to teach you various techniques would suffice. This would be really though, since most clans guard their techniques (at least the teaching aspect) quite a bit, and doubly so for ronin. I also believe that getting a level in a path is tied to your insight rank, just make sure that a path level is comparable to other paths of similar prerequisites. One thing you might want to look out for is that you get access to attacks as simple actions around rank 3 or 4. Also, because it just crossed my mind, you might want to make sure your thinking of a path, and not a school. I believe paths have around 1 or 2 techniques, something with 5 techniques in it is comparable to a full on school.