Duo Purchasing options confusion

Hello everyone, Apologies if this question has been asked before but I just wanted to make sure since iPhone duo preorders start next week. I am currently on the Tmobile Experience Beyond Plan (not 2.0) and I got a 17 pro after switching from ATT to Tmobile this year and I am at the 50% mark where I am eligible for the yearly upgrade now after confirming on my Tlife app. I get monthly credits applied to my EIP so I don't really pay anything for my 17pro. My question is when the Duo comes out for pre-order, do I purchase directly from Apple and connect my Tmobile account to start a new EIP or do I have to purchase directly from Tmobile? I am not sure what happens to my current 17 pro EIP since I am trading it in to get the duo and I don't even know if apple will let me purchase the duo since I still owe 50% of the phone. I am eligible for an upgrade at Tmobile but not sure if I will be allowed to trade it in at apple and get the exact same results as if I purchased the duo from Tmobile directly since I still owe money on the 17 pro. I want to get the duo on launch day and I think purchasing directly from apple would be my best option but I do not want to mess up my EIP. Does purchasing direct from Apple with my Tmobile account connected wipe out the remaining EIP on my 17 pro after trading it in and buying the Duo or do they not have the ability to do so? If anybody could help me out and point me in the right direction on how to purchase the duo on preorder/launch day and whether to purchase directly from Apple with my Tmobile account connected or buy directly from Tmobile I would appreciate it. Thanks. Edit: Looks like I would need to go direct with T-mobile to use my yearly upgrade program and to wipe out the remaining balance on my 17 pro EIP. Also does anybody have info on what promotions T-mobile is offering on the Duo with a 17 pro trade in?