Maxed out MacBook Air is a good idea.
8GB RAM for dealing with large pictures, multiple pictures, programs
i7 for boost in speed to get things done fast.
More disk space so you don't need to bring a external drive with you everywhere. Just get a thunderbolt 1TB drive and store all your finished files there.
I use Photoshop all the time with my base model 2014 11". Works fine. Depends on what size files you're working with, how many files, and what filters you're using.
thanks for the replies. Makes me feel more secure about getting the air.
My photo files are up to about 120 MB
I use Topaz and Nik filters plug ins if that makes a difference.