Making a real version of the song from scratch takes quite a bit of time. Generally a lot of people convert existing arrangements made by other people. If there is a full music sheet MIDI file that includes the entire band/the correct pitch/right tempo, then you should be able to convert it.
However, if there is no such file available, then you're going to need to do the process entirely on the editor you're using (ie. 3MLE). The reason why this is a time consuming process (unless you're some kind of musical prodigy who has a great ear) is you have to constantly replay songs over and over again as you simultaneously represent the notes required into the 3MLE or whatever editor you use to do it. A program like 3MLE maxes out at 16 tracks though which is extremely suffocating thus it makes the entire process of making a full ensemble sounding realistic extremely nuanced/tedious work.
Hope linking YT isn't against the rules. The only person I know who makes full on 10-person ensembles themselves from scratch like that is this person on NA East (and her friend also does this as well)
Most of us are just converting MIDI's into MML and that's about it; just optimizing the coding for the MML. If you want to at least be able to convert MIDI files to MML code, I suggest checking this post out
As for learning how to do it like this composer did, that's going to take a lot of trial and error unfortunately and a lot of time/effort.