Lcs and i pad ios compatability?

An iPad 1 will still run the latest version of the Lionel LCS App. 

Just remember, the iPad battery is NOT user replaceable, so a used iPad may have a nearly dead battery.  Apple has a service where they swap them for a reconditioned iPad for $99 (plus tax).  You can also voyage into the unknown and look at this iPad Battery Replacement Procedure, it's not for the faint of heart!

I know several folks that have bought used iPad units and had to deal with the dead battery in less than a year.

I still have an iPad 1 which works well with LCS. You can get an iPad Air 2+ though for 499 or 449 sometimes...might not be a bad idea since the 1 is pretty short on RAM for some other uses...and really slow compared to an Air 2. But again, that won't bother you with LCS.

I am using my iPad 2 with no problems. The comments above about purchasing a used one are correct. Mine is a replacement i got from Apple under warranty when the WiFi antenna failed while on a business trip.