Nice chunk of quilt!
How many tops you can expect to get out of a piece of wood this size depends on several factors, but most importantly the tools you have at your disposal to cut through the 8" dimension ACCURATELY.
If you have access to a large bandsaw, specifically set up for resawing with a good wide stiff resaw blade and accurate guides you could probably cut 3 tops that would finish out to .250" apiece. That's assuming the wood is flat, square, dried to under 10% moisture content and doesn't warp out during the cutting process: the ideal. Realistically though, you should probably go for 2 tops. How thick they'll end up depends on how accurately they can be cut in the first place. After that, you can sand them to whatever final thickness you want on a large belt/panel sander.
Obviously, the tools mentioned above are way, WAY outside those typically available to the average person, but you might be able to find a WW shop in your area that can do the resawing & sanding for you.
One significant caveat: DO NOT attempt to hand-saw the tops. That's a guaranteed disaster.