Is there a minimum # of paid lines on Simple Choice?

I have the Simple Choice North America 10GB plan with 4 paid and 3 free lines. I originally signed up for this as a 4 lines for $120 plan. Will cancelling any of my original 4 paid lines cause any problems? Will going under 4 total paid lines cause any problems? I want to take advantage of the current BOGO line (assuming I am eligible) and in one year port 2 of my current 4 paid lines out then right back to these newly opened accounts which should take me from 4 paid 3 free to 3 paid 4 free. I want to make sure this doesn't cause any issues with my plan.

Is there anything stopping me from doing this over and over as new BOGO offers are available?

Thanks, and hopefully my question makes sense.