Can anyone recommend what weight fiberglass cloth to use when glassing over a foam mold (that will be removed.) How many layers to make a sufficiently strong but light hull? Also, is it best to try to do the whole hull in one sheet or multiple strips? (i.e. is the rule-of-thumb to use fewer sheets and thus fewer seams to deal with later?)
eikelben,
Hopefully Dick Lemke will chime in, as he has a lot of experience with that construction method.
In general you want to use whole sheets of glass if you can. It’s harder to do, but generally produces a stronger hull. If I was making the hull I would use 2 layers of 6 oz. cloth, and then ad reinforcements around the high load areas. However it should be noated that i alwas over build things. 
HI dan - good to hear from you again.
I used 2 layers of 4 oz. and found a bit of “oil canning” on the larger, flatter surfaces. It isn’t large, but can be noticed when picking up the boat by the main hull. My big cat also did that, so perhaps it isn’t a problem. Add reinforcement around dagger and rudder areas, and of course where deck fittings and cross beams attach. If you are stepping mast to bottom of main hull, a patch of carbon - or even a plate/strip wouldn’t be a bad idea.
Keep in mind that the curves on the hulls add strength - so you can’t compare to a flat piece of two layers of cloth. You can always do a test layup on curved piece of scrap foam. I am posting on a different thread, that the foam float for my F-48 hull weighed in at 5.2 oz. and I plan to try leaving foam in, using one layer of 4 oz. glass as it will be backed by foam. Will have to get a weight on that when glass is applied.
The only reason I like 4 oz cloth, is the weave “disappears” easily with one coat of resin (2 at most) so weight is reduced. Larger weave on heavier weight cloth requires more resin to fill - thus a marginally heavier boat - but sure don’t want to argue that point. Paint adds weight too ! 
It may be hard to wrap an entire hull with glass and keep out puckers and folds. I would lay up half hull with thin tape along the seam line. Using single piece you will go nuts trying to get it to lay flat especially around the bow and transom areas.