If this helps, I shoot with 3 580EXII and a 430EX. You can get less expensive flashes that work really well. The child in me insist upon Canon. Rarely with interiors have I needed more that 2 lights though. I fire them with an ST-E2. It has always worked for me, but I'm going to invest in radio triggers soon, just to be sure. Softboxes and shoot throughs are very important, they cut down on the hard shadows that don't look natural. It wasn't mentioned before, but obviously stands. A smaller stand, (18" or less background stand), will come in handy for snaking some light on the bottom of chairs or under tables.