Rights and Attribution When Quoting Others' Work in Your Own

It's important to note that there really aren't copyright attorneys hanging on this site, and laws also differ between countries. And in any case, anything having to do with sharing scores on musescore,.com really is more suited for discussion over there on that site.

That said, in general, the most common advice you'll hear is that borrowing chord progressions is always fair game as it's practically unavoidable in tonal music that there will be largely chunks of similarity to pre-existing music. As for borrowing melody, that's tougher, and you'd really need to look at existing court cases to see which pieces have been found in violation and which haven't (eg, famous cases like "My Sweet Lord" vs "He's So Fine").

Also, whether or not you make money from a piece has very little to do with whether it is a violation. Consider, giving away exact copies of something for free is far more damaging to sales of the original than if you tried selling it for the same price (or higher).

As a separate matter, musescore.com does have license agreements with a number of major publishers, so even if your piece is considered "derivative" - even a verbatim transcription - it might well be allowed there. Again, that is all for discussion over there on that site.