The Explorer can only run up to Three engines at the same time. The features of the Standard and Premium version of the app are restricted and not usable on the the Explorer. All of the Free features are still usable.
The Explorer itself is designed to power the track that operates the engines with a Max of 6 amps of power (AC or DC). The input power uses the same barrel connector found on the MTH brick power supplies, the Z-1000 brick (without the Z-Controller) is an excellent power source.
All of the new RTR sets include the Explorer.