Basement sizes on Long Island are usually good size (Sometimes as large as the whole house minus the garage). Don't worry about it and do what the other poster said. Make sure the above ground living quarters are what you want and need.
The fact that there is a basement is always on my house list, and finished even higher, but concentrate on other parts of the house first.
You can design a layout to work in just about any space and that's part of the fun.
