I'd just get the base model, unless you want to do anything really flash, there's not that much between 2.1GHz and 2.4. You could also add more RAM later (buy it yourself, lots cheaper than from Apple).

In terms of keeping your stuff, when you get a new mac, connect it to your old one in target disk mode and use the Migration Assistant utility. It copies your login, applications, files, settings, everything you want from the old mac onto the new one for you. All you have to do is sit around and wait for a while