I would suggest that you look at other successful designs for clues. I would suggest that you look at designs from the hand-drafting days. If you are going to draw a boat and have never designed one it can be helpful to look at existing successful designs for get sense of proper proportions for dimensions and weights. For example, a mast on a 45 footer would be closer to 60 feet.
You might want to look at something like Farr Yacht Design
which was a successful design from the hand draft days and which was a simple design to draw and understand.
As to full vs fin keels,stability comes from a range of factors and the choice of either keel type has no direct connection to the stability of the vessel.