I'm wondering how are the terms of music theory in Esperanto.
Notice that I'm from Croatia so there are differences from English music, like, I say H instead of B and B instead of Bb. I also say C1 for middle C, little C for the C bellow the middle C and big C for the C bellow the bellow middle C. First, second, third, etc.th degree is NOT equal to 1st, 2nd, 3rd, etc.th as in intervals. In Croatian, I say prima, sekunda, terca, kvarta, kvinta, seksta, septima, oktava for intervals. Triads are kvintakord-s, 63chords are sekstakord-s and 64chords are kvartsekstakord-s. Dur is major, mol is minor, but that's only with scales. Big is major and little is minor regarding intervals. "Big-durish-septachord" would be major minor seven.

I really hope that Esperanto is similar to Croatian (because English mixes major and minor intervals and scales as well as enumerations of degrees and intervals while in Croatian it's much simpler) in the way of music, but if it's not, please tell me what are the differences.

You might find Bertilo Wennergren's glossary of music terminology to be useful. I haven't looked at it in detail but the section "Gamoj, tonoj, taktoj" might be relevant to your questions (and if you read his page and still have questions, he is normally responsive and helpful if you e-mail or Facebook message him with a question).