You have to decide what you are comfortable with for limiting how many prints are made, and then stick with it. As for the question about getting a neg via inheritance, any prints made thereafter wouldn't be as valuable because they won't have been made under the direction of the artist.
The idea of a limited edition come from printmaking... etching and the sort, because the etching plates get worn down after several passes through a press, so by nature of the medium it's limited. The idea for use in photography came about for marketing. Clearly, though, the fewer prints you make, the more valuable each print.
Some folks will do, say 5 prints at 20"x24", 10 prints at 16"x20", 25 prints at 11"x14", but I think if you change the paper you are printing on and start a "new edition", you will devalue your prints. In other words, it's fine to have a few different editions at different sizes, but if some are on Ilford paper, and others on ADOX, then you shouldn't start another edition with a different brand of photo paper.
Of course, there's nothing wrong with not editioning your prints. I don't think Penti Samallathi (sp??) makes limited editions.
So, whatever you decide, you should live with, and keep good records. It's good to know where your work is, if possible!!