Before I get my long tube header for my 99 2.4 z, I need to get a flex pipe and reducer. The collector on the header is 3 inches and I want to go down to 2.5. Question is, would it be better to get a 3 inch flex pipe and put the reducer after the flex pipe to go down to 2.5? Or should I get the reducer first to go down to 2.5 and then get a 2.5 inch flex pipe after the reducer?

just so you know 3" flex is ussually really stiff.... as long as you have the flex as close ask you can to the engine ull be fine....