From what I gather, hooking up stuff to the Air can be a bit of a pain (like to hook up a network cable you need a Thunderbolt to Ethernet converter), because the unit is so slim, they can’t fit full size connectors in for everything.
For me the maximum size of 13″ would be a deal-breaker. Old man with declining eye-sight I don’t want 17″ because of the size, so I make do with 15″, but I couldn’t handle 13″. That’s just me though.
And whatever MacBook you pick, be aware that they are notoriously low on USB ports. 2 max to be specific. And in a DJ environment that might be a bit tight. I have moved my standard to using a powered usb-hub which I have fixed in my flightcase and permanently attached my controller, external SSD drive and DMX-cable (Cuelux). I just plug in the one USB cable into my MBP 15 and am good to go. If I ever need to plug in something (extra LED light or USB stick) I’ll use the second port on the laptop.
Greetinx.