Do certain tip shapes give the bow/limbs more speed or make them smoother?  If so what are some of the guidelines?

Recurved tips add zip to the bow and soften the recoil. Narrow tips reduce tip weight which adds speed and lessons hand shock.

The angle that you cut the string grooves also plays a part. When the bow is strung you want the loops of the string to be in a straight line with the rest of the string if possible.

I have always heard that more material past the string groves is just more weight that needs to be moved.  I usually keep mine fairly small, yet functional and attractive.  If they are too small, I always worry about the string slipping off.  I try not to keep them too long, but I always build up the thickness with horn or wood.  This is somewhat for protection but also to keep the string where I want it.

AkBillyBow