Other than having to get a new tune for the 2016, that sounds like a good plan. Keep in mind, depending on the tuner you go with, you may have to pay unlock/re licensing fees to switch the device to another car.
As for the 400 awhp mark, I think that is easily achievable with the mods you have planned.
I am running stock plugs, 3 bar, 170 stat, SW catless downpipes, stock catback with resonator replaced with X-pipe, and mufflers replaced with summit race mufflers. I also have an Airaid CAI, AJPTurbo Tune, and run E20 gas (so I get a bit more spark). I also have the wastegate boost regulator mod. My car put down 369.4/451.4 on the rollers this past tuesday, with the wastegate on my intake wide open, so it probably had atleast another 10-15 hp in it.
Add ATP's to that and you should easily hit 400 awhp.
For comparison, I have attached a Dynograph showing the comparison between my car, with the mods listed but no tune enhancements, my car tuned, and AJPTurbos car (stock tune with downpipes, and CAI, stock stat, stock plugs, 2 bar MAP; as well as a power pull on his car with the same mods as his stock pull, but tuned - he got past 400awhp without the ATPs)
Hope this helps!
Note: His pulls are labeled. For my pulls, run002 and 003 are power pulls and 004 was my stock pull. He ran 93 octane for his pulls, with higher boost than I am tuned for, and slightly lower spark. I ran E20 with lower boost, and higher spark. Our stock pulls are very similar. Also, I used SAE correction so it is apples to apples and removes temperature, humidity, and ambient pressure differences.