LOL. There are hundreds of legal issues, involving corporate law, intellectual property law, privacy law, internet law and computer law. If you are going into this business, you need to retain a law firm with expertise in theses areas of the law----it is inconceivable that you could go into this business without retaining legal counsel---indeed, you may even need to consider hiring in-house counsel to assist you in this matter. There are no short-cuts here, and this web-site cannot be used as a proxy for the basic education you need in the law applicable to this business. If you do not have a budget for legal counsel---then frankly you are not prepared to go into this business.
Sound like a great plan, since setting up social media sites is such a pain. There is much to be learned, but consider starting with a few used books from Amazon or Half Dot. Startups, business , ip, etc. Often there for a dollar. It is just time to sign up at your local community college for some business courses, biz law, marketing, etc. In part you learn, plus you make contacts with your instructors and fellow students. You should consult an attorney to set up the business entity and "master contract," and insurance company for liability. Best of luck in the enterprise. By December you will know far more than you do today.
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Attorney Ross and Poulson both raise good points. Here is a start on some of hundreds of issues that Attorney Ross mentioned:
1) The best company structure to shield you from liability and obtain favorable tax treatment.
2) An insurance policy to protect you from the inevitable lawsuits that will come.
3) Your contract with the subcontractors, and whether or not you can shield yourself and/or your business from liability for their acts.
4 - 10,000 : TBD
It sounds like you have an interesting business plan. I would advise setting aside a bit of money to speak with counsel, but, as attorney Poulson pointed out, if you cannot afford legal fees, there are some reasonably good books on the subject.
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Other than the issues involved in starting any business (choice of legal entity, etc), you will face a number of intellectual property issues. Mostly, you and your clients will want a high level of confidence that you own and can transfer clean rights to what you create and sell. That means having good contracts in place with your subcontractors, among other issues. You need a good lawyer who can handle both business and IP issues. Good luck.