I did not use a USB mic with my raspberry pi yet, but one directly attached to the GPIO pins, but from what I heard a USB mic works but might have a bit more delay. Sound via HDMI worked perfectly fine for me
For the Display it’s important to have a good black, so the mirror does not shine a lot in the black parts (especially when the monitor is not covering the whole visible area. A high brightness would be good aswell, since the mirror makes it a lot darker.
Port location it would be optimal if they are not facing to the back, because the cables will make it quite thick.
I don’t use any nline voice recognitions because of the privacy issue. However I guess both should work with MM2. I guess the most important question there is wether you prefer one of them (or maybe already have hardware like echos at home, since it makes no sence to have multiple different voice systems at home)