Mba memory issue

In simple words I am a developer who is going to buy a 13 mba 8gb ram 128gb ssd. I am buying this as for the developer tools I can get on it.
I do not want the the mbp 13 as the resoultion is too low for me and I want a ssd.

But the question is how would a vmware appliance working on a macbook air on a external usb 3.0 5200 rpm hard drive work? Would it be fast and get on applications quick because there are some developer tools that I need windows for.

Just to be clear I do have a windows desktop at home and a linux laptop so I do not want a die hard windows person get in my grills   .

Many thanks

--Cavan