If you've not played with a backing track it might be tough first go around. Like playing with a metronome you have to be spot on. But I suspect you've done this before.

I'm not sure the sound from the laptop will be loud enough and may bit a bit unnatural. Also the speakers in lap tops are pretty "dry". Running it all thru an amp seems better. Can you add a bit of "colouring" if needed? Chorus, reverb, etc.. What are the room acoustics like? Assuming it's in a church the hard pews, floors and solid walls might make the need for amplification minimal IF the crowd is fairly small.