In a situation like this, the present church organist/pianist should be contacted regarding the organ for any helpful pointers, etc. This is an especially respectful approach to take. It's best to meet with this individual before the wedding day so that there aren't any surprises.
If the organ is locked, someone needs to be there that has a key or knows where the key is kept so that you have access.
Once organ is unlocked, you need to know where the power switch is. It's not always obvious.
When an organist approaches the organ bench, we slide onto the bench, we DON'T stand on the pedals.
Like a piano bench, you can adjust an organ bench to your comfort level by dismounting the bench and moving it to your comfort zone.
If you do play pedals, you play them with FLAT shoes. When you're not playing the pedals, you can rest your feet comfortably on the back of the bench rail.
You can place your music on the rack just like you would at the piano.
Before the week or day of the wedding, it's best to make arrangements with church personnel sir you to show up to practice on organ so that you can get the organ sound you're needing, prior to day and of wedding.
FYI: There are preset buttons under each manual. Choose one of the manuals and try each preset button under that manual. Play a couple of measures from your music. You will be hearing soft and louder to much louder as you go from one preset button to the next.
I would do this with each manual and presets. These have been set by an experienced organist, so I know that you'll find something you like.
If you don't hear one on that manual, go to the next manual and try each preset button.
Continue to do this, until you hear what you like..
The day of the wedding:
The pastor will take his place which is the que for the groom, best man and other groomsmen to take their place by the pastor.
I always got a signal from the wedding coordinator that all was well and ready.
I played the "Trumpet Voluntary" for the bridesmaids processionsal down the aiisle and get into place.
I started the Wedding Processional only after the bridesmaids were in place up front and bride and Dad were standing in place at back of sanctuary.
When you play that octave F intro on the organ of the Wedding March, that's the signal for the congregation to stand up and turn toward the back of the church to watch the bride and her Dad start processing down the aisle to the front of the church. I rarely ever had to go to the second page of the Wedding March. The organ sets the tempo for them to walk down the aisle.
Once they are standing in front of pastor, you can delicately end the Traditional Wedding Processional.
If you are responsible for playing the traditional Wedding Recessional. After the pastor says
"I now pronounce you husband and wife. You you may kiss your bride" the congregation rises and applades and then the traditional Wedding Recessional is played.
Best of everything and most of all, have fun!