Not that hard. Just promise to follow his five rules (describing them in your own words when you do to prove you understand them) on his minecraftforum.net thread. As for the "not allowing others" parts, he doesn't expect you to enforce them, just make sure the downloaders know his rules. Railcraft is the hard one, since, while you don't need to ask permission, they require a page showing all the mods, including links to their forum pages, download pages, and proofs of permission.