UT Tickets do not affect Magic Bands. Enter the Ticket numbers directly into your My Disney Experience account.
I have bought UT tickets many times and never have a problem. I prefer to order the actual ticket card from them and enter the # myself rather than the eticket.
You always have the option for new Magic Bands to arrive for each trip on site.
You will get an email when it's time to finalize your FP choices (you probably starting making them 60 days prior to trip) and Magic Band color/name and to make sure your address is correct. You will receive the Magic Bands quite soon thereafter. Mine usually come within 2-3 weeks.
I like split stays and do them often so I always Opt Out (you have a choice) of the Bands for the next resort I move to.
Just curious, how would you enter it if you did an eticket? This upcoming trip will be our first time purchasing from anywhere other than Disney directly so I'm trying to get all of my ducks in a row. Thanks!