For the donor's tax return, the only limits are those that generally apply (whether it is a 20% or 30% or 50% organization), and limits on schedule A deductions at very high incomes. It doesn't matter if a a large amount is donated in one amount to one organization or several smaller, amounts to different groups adding up to one large amount.
For general rules and principles on charities, charities need to avoid self-dealing. For example, a rich person could not make a large donation to an organization on condition that the organization hire their spouse for a no-show job, as a way of getting a tax deduction for the "donation" which is really a gift to the spouse. There can be implications when one board member or founder has significant control over the organization if that person uses the organization to benefit themselves. But that is more of a legal question.
