Recessed vs flush/flat is fitment, eg one from a Taurus is a recessed, one from an Escape/Fusion/F150 are flat. If you currently have MFT with the 8” screen you’ll carry your brackets over to the Sync3 screen, if you’re doing a 4” to 8” conversion you need to make sure you get F150 brackets.
G/H series APIMs can be problematic, for the most part the difference between the J/K & some L series is the firmware/calibration. There are some models of the L series that have a the same version of the eMMC chip in them as the M/N series APIMs, you’ll see them referred to on here as “MY2020”. The firmware in the L series is the ”same” 1U5T-14G374-Ex regardless of the version of the eMMC, the iteration just incremented by build date, so your unit can have say -EH and be flashed up to -EM. There’s also no runtime clock that tells you how many hours the APIM/screen were on, so mileage doesn’t really translate, you could have an APIM/screen from a donor that only had say 40k miles on it but there’s no way to tell if a lot of time the car sat idling.
In general when you do an non-Sync3 vehicle mod to Sync3 you’re better staying with a J/K series and you can have issues with the firmware in newer APIMs even if your vehicle came with Sync3 from the factory (eg with my 2018 Fusion which was on 3.4.x I dropped the same config into J & K series APIMs without any issue, went to an L and my heated cooled seat buttons stopped working, both on the screen and the physical ones. Remove them from the screen the physical ones worked, final resolution was to update the firmware in the FCIM aka HVAC control panel after that they worked).