I would go with a 36 holer for sure with a front disc. More so if using a big rotor. Our last tandem had a 203mm rotor up front and on steep decents at a pretty fast clip I could get the back wheel off the ground. I sure miss that stopping power. Not sure I would go that far with a carbon fork. The Winwood disc fork with a tandem rating only accept's a 160mm rotor, and probably not much better than rim brakes as far as stopping power, but, no heat on the rim. A rotor this small would be rendered useless on a steep decent in a very short time, and may warp quickly. Just a guess, but I've run a front disc for years on a Cannondale with a steel fork and a 203mm rotor. The ultimate stopping power, with a rim brake on the rear.