I just want to chime in here quickly and point out something very important: If you're stil in the process of learning, do not concern yourself with Amazon EC2 or "scaling". First you need to make things work. Trying to wrap your head around concepts like elastic cloud computing, scaling, and optimization are just noise to a beginner.
Scaling problems will arise if and when you have enough users. When that happens, you'll need to figure out the bottlenecks. At this early stage, you should resist the temptation to guess how your application needs to scale and just focus on building it.