Picturing the Decor ?

We have a ton of different décor options that we have rented and lined up for the big day , and we are starting to collect some stuff for DIY. But I feel im getting lost in what will look good and what we have and what we need and what we don't. I just cant picture what its going to look like with what we have ! It is driving me a little crazy thinking I am not going to know how anything looks or what we may be missing until a couple days before! I try and go on pinterest and say "okay well we have that so that's what itll look like or we should get this to add , it will look cool" but even then , its still just a jumbled up bunch of décor that I cant see the big picture with ! Anyone have any suggestions on how to move past this ? im afraid im not going to get what I want out of it , or im going to buy too much because im worried !