In answer to your statement about having pref parties and rounds and such I would assume you won't have those because it sounds like your formal recruitment will be in the Spring. Fall recruitment will be just a series of parties that each of the chapters have. The level of structure that informal recruitment has depends on the school. Some school keep it fairly structured and require girls go to every house at least once and others make it a free for all and let girls do whatever they want. In regards to the recommendation letters, it never hurts to have them and it shows the chapters you are really taking it seriously. Even if rush isn't that strong at your school if the chapter are close to total they may only be able to take a certain number of girls and better safe than sorry. Anyway, that's my opinion!
Good Luck!