Jwalker
Hello & Welcome to the Forum.
l am guessing you are refering to the Lionel O set.
Yes, you can add cars until you make the wheels spin(break traction) on the locomotive.
Many folks run their trains' consists as they would have been in real life. .
Some folks want to see how many cars their locomotive can pull.
lt's your train. run a consist that makes You happy!
Merry Christmas...
Happy Rails!
dave...