I agree --- the one in the middle is distracting. Don't worry about adding more patterns and colors. As long as the prints are the same style it won't get too chaotic. (which is what would happen if you leave the middle fabric in --- see - you knew it all along) And after the final quilting is done, it won't seem chaotic at all. It will be beautiful!
Design boards are nice - mine is a large piece of insulating foam that I got at Home Depot (about $10) I used fleece to cover my board. My board just leans against the wall instead of being attached. Fabric will stick to it or I use pins when it is being pieced and starts to get heavy. A design board allows you to put the pattern together, leave it, live with it, move things around --- What I like the most about a design board is that I can move all the way across the room to look at it - and I squint. It helps to just see the color value and not the patterns in the fabric. If you do a search for design boards - you will find a ton of suggestions on materials that different board members have used to make them with.