Catamaran design questions

I'm an amateur enthusiast, working on designing my own cruising cat, and I've got afew questions...

Having been considering several construction materials, I'm still trying to work out which might be most cost-effective while also being reasonably sturdy and safe for blue-water extended cruising. What can you tell me about the benefits or disadvantages of...marine plywood with fiberglass over, fiberglass alone, composite?

Using a tape measure and my own home as a rough guide, I've been attempting to plot out exactly how much cabin space I'd need in the hulls to be comfortable. Some friends say 8' wide by 15' long, others say 6' wide and 20' long. I'm expecting to use just enough space for a double-berth, a small sofa, head with shower. What dimensions might be "ideal", without being too big? Trying to keep this cruiser at or under 50' if possible.

I've been trying to work out a retractable daggerboard design for each hull, but obviously the cabin space might get in the way of this. Is there any way the daggerboards might be inward in the cross-section rather than dead center of each hull? How might that effect overall performance? Trying for a reasonably efficient design for offshoring that can also retract some for shallow water or for hauling.

Also, just any design tips or advice would be greatly appreciated. This will be my first multi-hull, if that matters.