If the atmosphere inside Aero seems chaotic, there’s good reason. Aero, located in a vast second floor SoHo loft, is many things: interior design studio, architectural office, antiques shop, contemporary furniture showroom, art gallery, literary salon. You can walk up and spend $25 or $25,000. Whatever it is, Aero is a success story. Since the day three years ago when partners William Sofield and Thomas O'Brien opened their doors, they were hot, and have only gotten hotter. They now have an impressive array of projects under their belts, from funky studio apartments and grand penthouses to a 15.000-square-foot shingle-style house in Maine. Having just completed the guest rooms in Peter Morton's new Hard Rock Hotel in Las Vegas, they are now at work on the forthcoming SoHo Grand. For Donna Karan, they have designed packages as well as boutiques in Geneva and Singapore.