Congrats on your upcoming wedding how fantastic!!
A signature quilt will be a wonderful way for you to read what everyone thought. Your colors sound great and the ivory will work well for the actual blocks your friends sign.
Am I understanding that you want quilt made "before" wedding so friends can sign actual quilt? If that is case then I would suggest against that. Main reason why is people/person as AliKat pointed out will mess up what they want to say at least once and then you quilt will not be what you envision. Just picking out a patten and cutting which squares that will be the ivory for signing will take you some time. You don't want to put too much on your plate with when you are entering the 90 day count down zone. Also kids tend to run loose while people are findind their proper seats I have seen flowers get knocked down and ruined would hate to see your wedding quilt end up on floor.
AliKat has great suggestions for the signing station--I would use those as a guide. Do you have a wedding planner he/she might want to know of this plan as well. I love wedding and everything about them I can't wait to see your quilt--it really is a great memory maker. Enjoy your wedding planning :-)