Thanks for all the info lads, much appreciated.
The problem I have is that I am trying to get these tracks onto an old iPod 5th generation device (the first video iPod I think, about 10 years old now but still going strong).
The actual wedding is my own wedding and we wanted to have music playing throughout the day whilst people are mingling, eating dinner etc. The venue have the facility to play music either via CD or via iPod. As we have so many tracks we want to play it's not feasible to use CDs.
I paid for Spotify premium last night (the 0.99 per month deal) but as people have mentioned, when you download tracks you are only downloading them to the Spotify app, which you can then listen to offline if needed. My iPod is just an mp3 player.
Neither myself or my missus have a more up to date iPod unfortunately. Think I may end up just putting on 'Now That's What I Call Wedding Music Vol 25' LOL