Track power vs Battery is the holy war of Large Scale. I'm a track power guy. I started last year knowing zilch, and now I'm in way over my head!
The Aristo RS3 will run out of the box on conventional DC track power--just lay some track, attach it to a power supply/throttle, and you're off and running. It's a good engine--I just ordered one myself!
The RS3 also has a "plug and play" socket for adding decoders. A decoder lets you run the locomotive by either wireless remote or by DCC (digital command control, more about that in a few lines). With a decoder installed onboard, you can run one or more locomotives independently. To do this you need to buy a decoder, (which could also be called a receiver), and a transmitter. Most transmitters can send signals to multiple decoders.
Some people like to run on batteries. You put batteries either in the loco or in a trailing car, and then the batteries feed power to a decoder, which then gets your signals about speed and direction from the transmitter. Batteries have many advantages but I've never installed them or really run an engine with batteries so I've got no knowledge to share. Tony's RCS systems are very highly regarded, and the aristo locos are configured to accept batteries from a trailing car--you just throw a switch. Aristo will sell you the battery car with battery, ready to go. You would need to buy a transmitter and decoder--from RCS, as mentioned, or the one I like a lot, QSI, which has sound built in. I' not sure you could fit batteries in the RS3, bt I've never tried
You can also use DCC. DCC systems put a steady voltage on the track, say, 24 volts, and then use the track to send digital signals to the loco. These digital signals can control a remarkable range of stuff--DCC is both complicated and extremely sophisticated. I use a version od DCC and to be quite honest, really still don't understand all it can do. But I'm having fun learning
You can use track power outside--probably most people still do. It has, like batteries, advantages and disadvantages. You need to make sure of continuity between track sections, and you need to keep the rails reasonably clean
I've ended up using constant voltage DC and wireless remote. I have 8 locos sitting on the rails mostly in a car barn, and can run them all independently. Some of them are run on Aristo's 75 mhz system, which is now discontinued, and some on QSI/Airwire. I just walk around with the throttle and run them in and out of the barn.
