The key thing to remember with Spotify is to DOWNLOAD your music to your devices or make your playlists available OFFLINE the day of the event. This way you can use both players at the same time and you don't have any issues of not being able to play a song because internet access has been lost. This needs to be done with each individual playlist, while still connected to the internet.
To download each playlist in the desktop app click on the down arrow with a circle around it next to the play button and wait for all the songs in each playlist to download. You will see the down arrow with the circle around it on tablet and phone apps as well, although it might be in slightly different areas.
With your playlists downloaded you can operate each player independently of the other players.
You can get at least the first month free. Sometimes you may need more than a month. About 2 months is usually enough time. You can always compile lists of songs somewhere else and then when you are 1-2 months away start your premium subscription with Spotify and start making your playlists.