I have several questions about bulk-loading slide film.

Do photofinishers need to know the ISO of the film in order to process it? I don't know much about E6...must I use properly DX-coded cassettes?

If I send my film to Dwayne's in a re-loadable cassette, will they send the cassette back with the film?

Is it important that I cut the film leader to precisely the right shape, so that it works with their machines?