I don't know if the carbons will be more cost effective or not.I am a fan of carbons and have had great sucess using them but also never had a problem with aluminums.If you go with a pure carbon shaft remembe they won't bend,but they will break that's whats nice about pure carbons they are either straight or broken.
The carbon composite shafts which are aluminum core and carbon wrapped will bend just as the standard aluminums.I use Easton ACC's (carbon composite) for 3D as well as hunting they are a great shaft but they are expensive. Seems like alot of guys like the Goldtips,I've never tried them so I have no opinion on them.
Either way a carbon of some sort will gain you a little speed and I would say that they would last a little longer.

As for strings I prefer strings made of 8125.There are alot of good string materials out there 450+,8125,DF97.The only one I don't like is S4.
I have used the Zebra strings in the past on some of my Mathews,I have not found them to be noisy but I have found them to be inconsistent as far as length and also some seem to stretch alot more than others.
Winners Choice are a fantastic string I have a couple on various bows,mine are made from 8125 and simply don't stretch,they have stayed the same though 1000's of shots.