Sounds to me like you want a MacBook, or even a MacBook Pro, not an Air. The Air is aimed at people who basically want to do some word processing, web browsing, and the like. Light work loads with maybe the occasional moderate load. It's also for people who are willing to give up performance and expandability in favor of portability. Remember that the Air is essentially a netbook. What you describe is better suited to a full on laptop.
And to answer your other question, no, the Air's RAM cannot be upgraded later. The RAM is soldered directly to the logic board, same as the CPU. This is the way it's been since the first Air model, and it's unlikely to change any time soon. You could probably upgrade the HDD at some point, but the new Air's use a special form factor SSD from Toshiba, and any replacement would have to be of that same form factor.
I want to get an 11.6" MacBook Air. I decided against the base model since I definitely want the 128GB SSD. I plan to buy an external 1TB Hard Drive to store a lot of data on but want to make sure that all of my applications and important data all fits on my internal hard drive so I don't have to always take the external drive with me.
I looked at the $1199 model which has the 128GB but it only has 2GB and has the base 1.4Ghz processor.
Is there a big speed difference between the 1.4GHz and 1.6GHz option?
I have seen an option where I can buy it for $1399 and it gives me the 1.6GHz CPU and 4GB of memory.
I do a bit of multitasking and most of what would be done on it is web browsing, email, office (excel, word), Adobe Acrobat, Filemaker, and Bento.
For this use would 4GB be better than 2GB and would the 1.6GHz CPU help a lot?
One last question. I have often purchased my MacBook Pro's with the least memory available and purchased memory from OWC. Is it possible to upgrade the memory in the MacBook Air after purchase?

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