Firstly, I have moved the discussion to the Hardware and Performance forum. We get asked this type of question a LOT, so you may want to have a look through the forum discussions and see what the answer was previouly.
I would note that "3,000 concurrent users" is a big number. You need to be very clear about what you understand by "concurrent users", what they will be doing and that this number is somewhere near correct. If you get this an order of magnitude wrong then it either won't work or cost you a lot of money (or both).
My best advice is that if you are asking this sort of question then the best answer is for you to run a much smaller pilot to start with and gain some real-world experience.