Thank you for the move from Life and Styles to Mansfield Park boards, you are very skilled! ;-)
" it is the attraction between Crawford and Maria that throws Edmund together with Mary, that takes the Crawfords to Southerton."
Here I don't agree.
Crawford is a "professional heartbreaker" and seeks attractive objects but it could be anybody else, as his later target (Fanny) shows, and as shows what is hinted of his past history.
While Mary Crawford is really attracted to Edmund Bertram and nobody else, very early in their stay in Southerton, which is more to credit to their uncle the Admiral being dissolute, and their liking of their aunt Mrs Grant, than to anything else - anyway they did not know the Bertrams before arriving.