Hey t.e,
We're happy that you're starting the transition over to T-Mobile, we appreciate you! Some great advice has already been provided but I just wanted to chime in on these questions. You can definitely just move SIM #1 into the working phone and this will keep everything the same on the service and account. Most of the time it's fine to return the phone without the SIM, but you might want to take the unused SIM just in case it is required. I double-checked, and there aren't any settings to control the start-up sounds unfortunately but you can check in with the manufacturer to see if they have any additional info! (877) 817-1759.