Welcome to the wonderful world of bicycling. You have far more to learn than can be posted in one thread. A good starting place would be to check out the beginning/returning cyclist sticky thread in this subforum:
http://www.bikeforums.net/showthread.php?t=348528
I understand the desire to start out with a good bike that will last you for many years, but you are putting a lot of pressure on yourself to make a complex choice without enough experience to even fully understand the question. You will get a very good bicycle if you spend around $2500. But there are so many different types of bike to suit so many different purposes and preferences that it would only be by blind chance if you managed to pick the same bike now that you would pick if you had a year of riding in your legs before choosing.
We can help you choose a bike after getting a lot of information from you. But my suggestion, if you want to get a nice bike that will hold you for a while, would be to start with something inexpensive and then, after you have learned more about what you want from a bike, spend the money on a keeper.