I'm thinking about making the plunge into studio lighting with a Profoto D1 unit. I don't want to overwhelm myself with "too much change", so I'm going to start with just one unit. I have some basic umbrellas and I'm sure the Profoto umbrellas are a notch (or more) better, but I want to dive in feet-first and get a softbox to start. Question is: what size? I'm thinking a 2'x3', as it somewhat simulates the size/shape of a window, or I can turn it sideways and have a broader source. (Certainly I can and will buy more softboxes in time to get some size variety...) What size would others recommend?