Question about upcoming BOGO, Tmobile Deals, and going 7 line to 9 line.

Hi guys. Current plan: Go 5G plus + newer inside code from 2023, with 3paid+4free lines. I'd like to add a line (BOGO) to transfer my line from 1-8 to 9-12 lines. I know Apple is running iphone duo, in which add new line = 800 off for me. Can i combine this with BOGO (I need to get 2 lines). Is Costco still the best place to do this BOGO? (to waive 35 and get 150 GC) If i wanna combine BOGO + no-trade-in with new line 800 deal, do i have to do this at Costco in-store rather than pre-order online? When I do BOGO, will it move me to the 9-12 lines? I've heard some rumors of Tmobile blocking this before, and with Tmobile changing plans and rules at a rate of once a month (or at least it feels like it), I wanted to get the most up to date information. Is the 9-12 line still accurate? Per the calculator from one of the legends here, i should be moving from 148 to 144. Just wanted to make sure for the same reason (Tmoblie just changing things so frequently these days). My guess is that go5G Plus will become Magenta like now, with the new launch of this T-Mix thing, so I would like to add BOGO asap when it is actaully available. Thank you !