If you have a Legacy system the Lionel Layout Control System, LCS, can be added to the layout. I would start with the wireless module and then develop a plan for what all you want to control with the LCS modules. The LCS wireless can be connected to your home wireless or operated as a standalone wireless network. I have mine set up as an independent network. No connection to my home network router. The LCS app is for the iPad and an Android version has not been released. I would not try to put the LCS app on an iPhone, stay with the iCab app for the iPhone. While engines can be operated with the LCS app on an iPad it is not really set up for that purpose and full functionality is not available. If you are running conventional engines with your Cab2 adding LCS will not change that.
Using LCS on a modular layout that is set up and then disassembled for shows will present some design challenges and set up issues. It depends upon what is controlled from the LCS components and how many LCS devices and interconnecting cables there are. Lionel has not released a splitter, or Y adapter, for the LCS system. That means all the devices have to be connected in series from one end to the other end. It is not possible to route the connecting cables in two directions from a central control panel. My layout is modular but is not disassembled periodically. It was disassembled for shipping on a one (hopefully) time basis.
The system is fantastic when set up and running. I have no manual controls on my layout, only the LCS.