That's generally too many fonts for Font Book to handle. It's intended to be a light use font manager for the average user.
That, and the fact that it hung again while building a new database is a very sure sign that at least one of the fonts is damaged badly enough to make FB croak. When that happens, its database is damaged again, and the only way to fix it is to start over with the instructions above.
Make a folder on your desktop and move all of the fonts out of your user account into that folder. Then repeat the above steps. With what should only be the fonts installed by the system on your hard drive left, Font Book should then finish loading successfully.
Are those all, or most of them, free fonts? If so, free fonts are the number one cause of headaches like this. They're free because that's all they're worth. Not that there aren't some well built free fonts out there, but they are in the serious minority.
Figuring out which of those you have are junk involves adding a block of them at a time to Font Book and seeing if it dies. If it does, you know at least one font in that last group is no good.
You could also purchase a better font manager and ditch Font Book. I recommend either Suitcase Fusion 4, or FontExplorer X Pro. Both have built in font checking and will flag bad ones. I know Font Book does too, but it's not nearly as good. With SF4 or FEX Pro, you can check the fonts before adding or activating them.