Z-Stuff has exactly what you need and I have used their devices extensively.

You do not need a smartphone. iPads will work and are even more convenient to use. Apps are free.

With the BlueRailTrains app, I have worked out a procedure which allows two separate smart devices to independently control two BlueRail equipped engines at the same time. Am not sure if this would work with EZ-APP.

Stay tuned. Everything you are asking for is currently available in the new BlueRail product.

App based operation of model trains is definitely here to stay and is a serious wave of the future. One issue which is pointed out in this thread is that apps seem to work better with IoS than with Android. I currently run transformer based conventional, hand held controller (LC & TMCC) and app based  Once you get used to app based, it's really convenient to use and has the advantage of continuous feedback display of operating conditions.

Another option is the new BlueRailTrains/TamValleyDepot control board with a DCC decoder.

Williams engines with bluetooth or any wireless remote control system.

For various methods of train location detection, you may refer to my guides posted on the OGR forum in the electrical section.

For a deadrail installation contact Pete Steinmetz at deadrailinstalls.com.

Try Pete Steinmetz at DeadRailInstalls in San Diego, CA.

Williams locos with bluetooth control.

You can install the BlueRail board which is the heart of the Bachmann EZ-APP. I have done this successfully on eight OGauge locos and they all work well. The BlueRail website has details for this conversion.

These were taken the first day. I purchased the bluetooth circuit boards from BlueRailTrains who makes the boards for Bachmann and switched them out with the E-units. The BlueRail boards work very well controlling my OGauge locos. You can see videos of this on BlueRail's website (www.bluerailtrains.com).

Have three working Williams electronic Eunits with sound modules. These were removed prior to conversion to EZ-APP. Anyone interested?

I have two Williams locos battery powered with bluerail boards and one track powered as well. All three perform very nicely. This system is a major step forward.