As for Mods on the M2 there really aren't any mods that you will "Need" to do, this thing just runs awesome right out of the box. (so to speak, you do have to put it together) There are things you can print to make life easier like tool holders, fan bracket, etc. but its more of "wanting" different upgrade like the V4 then "needing" them you will be very satisfied with the stock M2. The only thing recommended is to print spare motor and extruder mounts just to have back ups. Other than that just put it together and start printing, you'll figure the "want" parts later on and if you run into trouble along the way there are so many helpful people here on the forum and Rick's customer support is top notch too.
Again welcome to the Club....

-Steve