I kinda always visualized a humanized Dash as wearing a bomber jacket over a flight suit (with an awesome, 20% cooler pegasus design on the back). Since pegasi control the weather, she'd be something like those pilots that seed clouds so it rains and stuff.
Applejack, of course, is going to be a cowgirl. Not the Daisy Duke type, since she's a rodeo girl and a farmer, and Daisy is busy distracting the law from the illegal Duke moonshining business. So AJ's got gloves, denims, a lariat, and of course her stetson.
Also, this is my ship, heh.
And did I mention I see Dash as Asian? Yeah, I said it. Southeast Asian.