First let me say I run Mostly MTH but also have Legacy. You will enjoy running both. Unlike others I will list what Barry's Book and MTH say you need. Lionel #990 Legacy Command Set #6-14295, Lionel LCS DB-9 Cable with Power Supply #6-81499, Lionel LCS Serial Converter 2 (SER2) #6-81326 and MTH TIU/TMCC Legacy 6' Connector Cable #50-1032. I originally did not add in the SER2 but trust me add it in as they suggest. This is the complete list they suggest. I would add in one more item. UPGRADE WiFi app from MTH to the premium app for $25. You can then run 99% of the LEGACY FUNCTIONS from your MTH WiFi App. You will enjoy running both immensely. I Also purchased the Legacy Crane Car but have not used it yet. You can also get Lionel Legacy Dinning cards with sound which is cool. You can, but I do not know why you would want to, purchase the Legacy Expansion Control Set but as I said you can use the MTH APP which is a whole lot cheaper even if yo had to go buy the WiFi unit and the app.
I am not knocking what others have said but we all tend to forget the cables and other items needed to make it work.
Enjoy your Legacy and continue with your Excitement and fun running ALL trains
