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[Too Tall]

Thank you

As Steve M says, The set has a power supply, so all you need is the app on a suitable device.
However the power supply included is pretty much bare minimum, so when you are at the stage of running 2 or more locos at once, it would pay to get a more powerful one.
If you wanted a physical DCC controller as well, that would negate the need for a power supply. So it would be best to decide how you want to do things after you have tried out the set and app control.
Some are happy to use the App alone, I prefer to use its benefits in certain circumstances, but control the old school way for shunting etc.
Horses for courses.

[IanS]

If you go down the route of the HM7k bear in mind that regular DCC fitted locos won't currently be able to be controlled by the system. You will need to ensure that the decoders are the new Bluetooth ones. Hornby have announced a dongle to convert regular DCC systems to be controlled by the app..

You may (or may not) be able to control locos on the same track by both methods. It's still not on general sale so I can't verify either way but it is 'supposed' to work. As mentioned above the Elite system from Hornby would be providing the regular DCC control and will be tested by them, other systems may work too and should work.

[Steve M]

Just to add to Ian's comment, the dongle has been designed to be compatible with the Select and Elite controllers as they have a built in Xpressnet port. Other controllers may have this interface and may work but compatibility across brands has not been tested.
The dongle acts as a 'translator' as it receives the commands from the app via Bluetooth, converts them to commands to the Elite, which in turn sends 'old school' DCC signals down the rails to non HM7K decoders. This allows both HM7K and legacy decoders to be controlled from the app.
If you have a DCC controller and the app then both systems can be used at the same time (unlike DCC and DC) so it is feasible to be running a couple of locos on say HM7K on the mainline while shunting via DCC in the yard - absolute flexibility.
TooTall commented that he preferred to use his DCC controller for shunting - have you tried 'creep mode' on the app?
As to availability, there are a handful of dongles under test (they work very well indeed) and we understand that delivery of the batch for sale is imminent.

[Too Tall]

Re: Steve M, creep mode.
No ... TBH I didnt know about that.
I find the app is a pain to "pick up" and drag the speed control slider from 0 throttle, so I tap 25% and then adjust to set the mainline loco's going, then use the Elite to control the shunter.
I do have the Dongle on pre-order, but like a lot of stuff, the release/in stock date keeps slipping !