The Ultimate Tutorial is outdated; start over from scratch and use Sappy and Mid2AGB to insert your music, not Blazer's method (which you should only use if you're a masochist). It's far easier and gives you better-sounding music.
If I understand correctly, you're trying to insert FE6 samples into FE7? Just use "Export samples" in Sappy, export them as .s files, then import them into your FE7 rom. Much easier/cleaner than copypasting in hex.
That being said, samples are just audio files (which tend to get gigantic quickly) at the end of the day, so it can happen that you have a huge sample that gobbles up several kilobytes every now and then. There's so much free space to work with that you shouldn't have to worry about running out, though.
Alusq's post in Music Inserting help? was marked as the answer