Definitely make sure to book your date with the resort. Once you pick a TA send save the dates out ASAP. Then begin doing your research of the resort (this should take place before booking and after).
I found planning easier when I sat down with my FI and we discussed what we want and don't want.
**** But first things first do not stress on things you can not change (guest attendance, attitudes, family, late RSVP cards and things being perfect).
Congrats and may you have a stress free planning.