I think maybe you should consider starting out with your item 3, forming a business plan...not for investors, but for yourself. Taking the time up front to think out how this business will make money (from either or both 'investors' and musicians), in what amount, and along what timeline is a critical step in figuring out whether this idea can really turn a profit.
Do the thinking and planning now, and you can focus on bringing in the customers who earn you more, and also create a real budget...deciding to spend $70k on a specific developer just because they said thats what it will take is silly...you need to know how much you can afford to spend.
I also think you need to consider different terminology for your investors. When you call them that, it implies that they are providing you with money in exchange for sharing in the company's profits. It sounds like you mean them to be some tier of customer, separate from the musicians, in some kind of matchmaking. Maybe you can call them Sponsors, or Industry Members, or something else for clarity?