Music and sound systems tend to get forgotten in the hustle and bustle of the ceremony. It’s important to be on top of this because it plays vital role.
Firstly, here is a good guide for the amount of tunes for the ceremony:
• 10-12 songs for warm up playlist
• 2 song for walking down aisle (one for walk, one for back up in case it finishes)
• 3 songs for signing of the documents
• 10-12 songs for after ceremony playlist
Regarding playing these tunes, I highly recommend you get the venue to do it. If they can’t, organise with someone who is close to the couple to play the music (make sure you organise this beforehand).
Also, there’s 15 zillion different phones out there and each of them have different connections and adaptors.
Make sure you are familiar with the phone or iPod being used to play the music.
Usually an AUX cord will do the tricky (not with new iPhone and Google pixels, though). Otherwise you can check out what adaptors are available to buy.
Finally. It also goes without saying that you should have a PA and mic for the ceremony (unless it's a super small crowd).
I avoid using wireless mics. It’s a personal thing, but I just don’t trust them because they can cut out. If you are using a corded one, make sure no one will trip over the cord.