Thank you all for your advice. Am "processing" it all as quickly as my inexpert brain can. (i'm a she, btw, but no worries it's not important.)
I would also reccomend the Pro, by the time you get the SSD size and the RAM at the same level they cost much the same.
Also if you want to save a few $$$ then a 2014 refurbished 13 inch rMBP sounds perfect for you....
Or B&H have good deals on last years pro, brand new, it'll be far better than a new air...
I would not reccomend one to one for file transfer when you can just back up your current computer with time machine to an external hard drive and migrate the data accross to your new one.
If you don't have an external back up buy one now and use it, your livelihood seems to rely on those files don't lose them.