Yes, it would be appropriate to start gathering letters of recommendation now. Schools have OPTIONAL evaluation forms. These are used instead of LSAC LOR forms if someone where to chose to do that. It makes more sense to go through LSAC so don't worry about those.
Dean certifications and things take no time and you can get those as soon as they are available in September. My one school that required a Dean cert got it in a week of me asking my school's office that handles that stuff to do it. It also isn't really a letter from your Dean like an LOR. Mine was a sheet that looked somewhat like a transcript with my class rank, majors, year of entering, stating I had never had discipline problems, etc. I imagine that different schools handle this in various ways. At my big state school, I just filled out a form and checked the boxes of all the different kinds of information I wanted the cert to have.