I don't know where you live, but here in the United States, the average internet connection isn't capable of downloading 1 GB in just a matter of minutes. About half an hour would be more likely. And the trend of people just tethering to their smartphones as their primary internet connection means a lot of people have extremely low data caps to deal with, so downloading 1 GB could mean using as much as half of their data allowance for the whole month.
And my game's gonna be about the length of FireRed/LeafGreen. So not exactly short.
8-bit music aren't stored as MP3s in the first place, they use tiny synthesizer formats more similar to MIDI than they are to MP3s. If you want your 8-bit music in full quality, you'd seek out these obscure formats instead of MP3 or MIDI. But MIDI isn't restricted to just piano, and is capable of producing a pretty decent rendition of these 8-bit tunes. You're able to record the exact output of these 8-bit songs as an MP3, but the MP3 version would be thousands of times the size of the original 8-bit version. You used Crystal version as an example earlier, but do you know how much data the entire soundtrack for that game takes up in its original non-MP3 form? 103.7 kilobytes, or about 1 kb per song.
The smartest solution then would be to include MIDI music with your game by default, so that it's a nice and small download. Then offer an optional MP3 soundtrack download available for people who would prefer a richer soundtrack to accompany the game. Or, if you've got the skill, add the ability to play the original chiptune music from the official games, that way you've got an extremely small download with music that sounds more accurate than even the MP3 versions do.