The portion of the daggerboard that is below the vertical center of gravity will add stability while the portion above will subtract stability. Since wood floats and aluminum doesn't, the cladding that is underwater will take away some of the stability that the aluminum adds. I don't have the information to calculate exactly what the stability change will be. It will change as you raise and lower the daggerboard to allow for wind direction.

How are you building the mast? Warp should actually be easy to control.

Laszlo

   To make the mast. I just cutdown a 4x4 on table saw. It was supposed to be Douglas fir but a friend has his suspicions. I'll give it another try when I find some spruce. 

   I built a mast for mine this past spring. I went down to the local lumber store and sorted though the hem-fir 2x8s until I found one that was straight and relatively clear, which of course was the very last board. I cut out two pieces from the best areas of the board, planed them down, and epoxied them together with the same side on the inside. Put another way, lay the board down flat and mark the bottom side. After cutting you glue so the bottoms are together.  This way if there is any tendency to warp they will be in opposition. 

Slash2 is exactly correct. Instead of trying to shape a mast from one large piece of wood, for small boats it's better to laminate masts from multiple pieces of wood so that the tendency to warp is canceled  out.

On large boats and ships it's feasible to use a single piece of wood because the thickness fights warp and provides a reserve in case of checking. Small pieces of wood lose the thickness that holds them in shape when cut (or even planed).

Follow his method and you won't have any warp in your mast.

Laszlo

 I forgot to mention that you need to clamp it all up nice and straight. I did as John Harris suggested: clamp the assembly against the bottom of a basement I-beam, aligning the mast edge and beam edge.,