Sagrada Familia

We would like to be able to go to mass on a Sunday and then take a tour. I have a couple of questions.

How early would you recommend being at the church to get in for mass? Where should we enter?
I would like to take a tour with a guide but I can't find a tour that includes the towers. Any ideas of where I can find this? If you had to choose between a live tour guide and going to the towers which would you choose?

Thanks