I think everybody has had most of those "buggerups" happen at least once - and those that haven't are merely overdue.

I usually pull the darkslide only about half way out, and place left index and little finger on the ends of the film grooves to guide the film in. This works great even withh 5x7" film, especially when I'm confusing myself with four 5x7" and four 13x18cm holders. Same confusion with 9x12cm and 4x5" holders, by the way...

As to tray developing, throw away the tongs and get a pack of surgical gloves instead.