AFAIK, FCE needs a firewire camcorder only for its 'log and transfer' import facility which is a nice tool.
I have a iMac 2.8GHZ and a Sanyo HD1010. I have to copy the clips to the filesystem and then convert via MPEGStream as FCE doesnt import my 60fps clips well. The only issue I can see is that 8GB of clips turned into 60 GB of 'AIC' mov files... so you will either need to film in a format FCE can edit directly, or buy a external USB disk or dont use HD!
I guess what I am getting at is that with or without firewire ports, there are many ways to get clips into FCE. A MBA will run it fine - my friend has a old macbook (intel) which is prob in the same ball park performance wise as a MBA (although I have no evidence to back this up - just speculation). He runs FCE just fine.
Neil