A sheet-music service would need a catalogue, search and access rules tied to subscription entitlement. Before development, the publisher must establish the rights to distribute each work and the permitted ways subscribers may use it.
Downloads, browser viewing and printing can require different controls. Catalogue records should identify edition, instrumentation and difficulty where appropriate. Users need to distinguish a full score from individual parts before choosing a piece.
Start with a rights-cleared collection and test finding material for a real rehearsal. Decide what access remains after cancellation and how corrected editions are issued. Software can organise entitlement and delivery, but it cannot create distribution rights or guarantee that downloaded files will never be copied outside the service.
Related reading: SaaS Platform Development: Turning Your Idea into Subscription Software.