Ryan overall the Legacy DCS programming side is outside of my wheel house, but it's something I'm definitely interested in following here. I can answer a couple questions you raised. Please see inside quote box and below it.
@rplst8 posted:I think TMCC engines have to be added to the Legacy remote manually, correct? Yes, but once entered, their information is stored in the Legacy base's memory and can also be saved to a Legacy memory module. In addition, there is no "confirmation" that the engine exists on the track in the TMCC world. It's unidirectional. Yes the 455kHz legacy signal is one way, from the Base to the Locos, etc.
I would think the process would be...
I'm not familiar with the worth @Ryaninspiron has done, but he may have some of these pieces already completed or started.
Here are links to @Ryaninspiron 's work with Lionchief and Legacy: