If you want to spend the extra money you can go DCC and add decoders to them, You can then program them to run together, if you are running identical engines DC is fine, but if you mix 2 different engines especially from different mfgs the speed diffrerence can either make one engine pull the other putting stress on the lead loco, or wearing on couplers, or if the faster loco is second it will push the first around the track causing stress on the motor, so safe than sorry make sure you run to identical engines and it will run great if you have the power.

I have a UP 4-8-4 and it runs ok on 18' if I run half throttle. If you run 22' curves you won't have much problem, and is also more reliable for pulling without couplers coming loose.  I run e-z track,and use 22' and 18' curves in the same turn to make it seem more realistic and i've had no issues. on 18' the driver trucks seem to derail at high speeds.