OK. Since the BY8001 MP3 module provides no guidance in this regard I guess it will be a YMMV.
One thing I know for certain is the MP3 processor in the module is NOT performing any kind of pre-fetch or caching of the beginning of the different MP3 files. That is, part of the delay in starting MP3 playback is the nature of the digital compression/encoding. I guess all you can really advise in this regard is to expect a small gap when starting/changing sounds...and to the extent possible construct the sounds to best accommodate this effect.
Separately, for background/layout sound application I think the instructions should advise on how to wire it up to start playing upon application of power. The closest example in the manual seems to be the Mixed-Connection diagram but that gets the trigger voltage from the +5V connector...and I don't believe the kit comes with that cable. Plus, it's not clear/obvious if the BY8001 player module is GUARANTEED to start playing if the trigger is present upon initial powerup?
2 other ideas on using the module:
1. Since the volume control is on the board, it may not be convenient to access in day-to-day use. So if this is a single-sound application like for layout background, you could simply create 3 different MP3 files with the same sound at LOW, MED, HIGH volume. Then via the remote control you can simply activate 1 of the 3 and you have remote volume control. Ta da!
2. And related to above, you could create a "silent" MP3 sound as the 4th MP3 sound. So if you want to mute the background sound simply press the 4th button and it will play the silent sound and stop so you have just muted the sound by remote control.