1. The TSX intake manifold and throttle body are an absolute direct bolt on and required no special modifications to make it fit. It's simply a bolt off-bolt on mod and is completely worth it. I have a 2006 accord too and had no problems at all.
2. The pulleys are my favorite "performance" mod of all. Even though I don't race, it is an accord after all, I LOVE the added torque and MPG's I get from them. I ordered mine from ultrarev.com. They will run about $200-230 If I remember correctly.
3. Retrofit all the way! I did them myself but ordered all the parts from www.theretrofitsource.com. Excellent products and hands down the best customer service. I have the morimoto 3five ballasts 5000k bulbs and Gatling gun shrouds. Also have XBA LEDs mounted behind the shrouds.