Item 3 is important in more ways than most people realize. Last year many farmers in my area that planted soybeans early had a problem with slugs eating the sprouting beans and were forced to replant multiple times. This spring I went to a growers conference and heard a presentation by a Prof. Tooker from Penn State Ag about the slug problem, which he has been researching for several years. Turns out that the slug infestation can be directly traced to the use of insecticides used in seed treatments. The insecticides kill beetles (and other beneficial insects) that eat the slugs but don't kill slugs because they aren't insects (they are mollusks). No beetles more slugs. Take away is don't use treated seed. However, standard practice at seed companies is to treat seed with fungicides and insecticides, thus creating a problem rather than solving it.
When I think about insects and slugs, then slugs are typically considerably larger and have more body mass. Is it only the smaller slugs or slug eggs that the insects eat? I have a hard time imagining a beetle eating a slug.