I like the tune a good bit, but I'll refrain from any advice about composition because the inherent subjectivity of the subject and also there are many other much more qualified people here to comment on such things.
BUT I do have considerable experience using guitar pro 5 for sequencing my own midis, so here's a few notes about the software:
Looks like you've already figured out not to utilize the RSE effects or playback engine, that is there for playback within GP5 and not really for exported files.
GP5 handles "individual" tracks in kind of a non intuitive way. You'll notice that when you add a track, it actually assigns two channels to the track. The reason for this is to allow for greater-than-one step pitch bends and certain other "guitar" techniques to actually playback correctly in General MIDI (which doesn't support >1 step bends) [EDIT: I kind of misspoke here, pitch bend range is technically decided by the synth, but the GM parameter is generally synced to +/- 2 semitones by most MIDI synthesizers) ex: Track 1 utilizes MIDI channel one for the first half of a two-step pitch bend, and the second channel to complete it. Obviously what this means is that your total amount of tracks are halved unless you assign the track to one channel. The trade off there is that if you try to utilize anything that might need that second channel (ie. large pitch bends, the wide vibrato, or whammy bar stuff) needs then it will not playback correctly, either in GP5 or the midi file you export. A good rule of thumb regarding this is that instruments with alot of articulation (say, a guitar, other stringed instruments, synths, the vocal/choir patches, and so on) could benefit from this, but anything that generally doesn't (pianos or other percussive instruments) may as well use one channel.
Vibrato and especially "wide vibrato" take up alot of space and I mean alot in an event list. Your exported midi file could bloat to be quite large if you overuse these.
Save often. GP5 has always been considerably unstable for me though I suppose ymmv. But better safe than sorry.
If you are using the MSGS wavetable for playback, then the Chorus and Reverb settings on each track won't seem to do anything, but they do work. The Microsoft wavetable simply doesn't support effects, but most other synths do and your settings for those parameters are saved in your exported midi file.
On that note, I'd recommend getting a softsynth set up for playback as opposed to the Microsoft wavetable. This is more for convenience and avoiding buggy playback, because while you should use whatever you think the end-user will use, the MSGS wavetable simply doesn't work or borks out on occasion. I personally use coolsoft virtualmidisynth and a roland GS based soundfont which essentially is the same thing as MSGS but with better quality samples and effects support. This has the added benefit of being able to switch soundfonts on the fly.
Using the mixtable is perfectly fine, it's more or less an interface for inputting MIDI commands and/or altering parameters. Everything it can do is supported by General MIDI outside of the RSE field.
I have a few other things I wanted to get into, but this is running long and my memory is goin fritzy. But i hope this helps a bit and if you have any specific questions about gp I can try to answer.
Looking forward to more tunes!
