Once track power it applied I want the have the led come on first and then the music to play. I would have make some kind of delay between the two. This was my original idea but comment is invited.
Well that's easy. Load the MP3 file into any MP3 editor (freeware/shareware) and simply add a silent gap of 10 seconds or whatever at the beginning of the sound, re-save.
The $1.07 MP3 player appears to re-start at the beginning of a single MP3 file when power is initially applied. By extension, you could add a, say, 10 minute or 1 hour silent gap at the end of the song so that for each application of track power, the song only plays once. Otherwise the MP3 player advances to any other MP3 files or restarts playing a single MP3 file if that's all that's on the microSD card. So, again, it's worth the upfront effort to talk thru exactly what you want to do. Measure twice, cut once.
I think you said you're running conventional? Well that too is a control system - so for example you could trigger the lights and sound whenever the Whistle button is pressed. Or toggle it ON/OFF with each the Bell button. It only takes about a $1 of assorted simple components (resistor, capacitor, diode, transistor) to make a DC offset detector. Or if you use uncoupling tracks you could activate the car by positioning it over an uncoupling magnet.
Or like GRJ is proposing you could add a wireless remote control to turn it on/off; on eBay you can get combo remote-FOB and receiver with relay for the boxcar for less than $5 or so.
