Andy, as long as you're 100% sure the MCII throttle that comes with the ESU CabControl is running Andoid 6.x not 4.x as discussed, then you should find it works great. And yes, it's a WiFi throttle only.
This way, you should be able to run any loco you buy that already has a DCC decoder in it, regardless of current draw. And you can probably find an older Weaver loco with a Pittman motor for a lot cheaper than a modern Atlas.
I'm not sure about the Lionel brick for 2-rail. The CabControl comes with the power supply, command station with booster and Wi-Fi inside, and one MCII throttle. Later you can add more ESU 7A boosters if needed, and they come with power supplies also.
Kadees come in "old" and "new" as well, like Atlas track. Old are in the 8xx series and have exposed jaw springs and are a bit less realistic-looking. The jaw springs are known to fly off during ops occasionally and you can never find them right away. They fly off so fast that they time travel into the future, so you will usually find them in the first place you looked, but only about a week later. 
But they work better on tight radii and are a bit easier to uncouple by hand with skewer etc.
The New are in the 7xx series. They look more realistic and the jaw spring is hidden, so they just work 100% of the time. However they don't have such a wide gathering angle as the Old, so not as reliable coupling under about 40" radius.
804 and 805 are the "standard" old Kadee and 740 and 745 for the new. There are other versions with over and under shanks, longer reach, and short ones for P&D F Units.
The best combo for brass locos is metal coupler in a plastic box for insulation in case the brass shell is "live". Metal coupler in a metal box is good for mounting on plastic.
