Yes, you can make multiple QCDs.  The sum of all of the QCDs during the year cannot exceed $100,000 and, if you have basis in nondeductible contributions in your IRAs, your QCDs cannot exceed the amount of your IRAs that would be taxable if all of your IRAs were fully distributed during the year.

Yes, you can contribute more or less than your RMD.

There is no minimum amount to be a QCD.