I've not checked this yet. You probably need to consult source code. In my opinion 200 bytes per variable should be fine. But just to warn you: nvram is limited in size. At most it could be 32k, it's now available 20k on my wl500g.
If you need store data in flash I'm recomending the following. Due to the different flash types there is an unsed gap in the wl500g flash which is 64k in size. It's at 0x3e0000. So you can alter the kernel, so it will map this 64k as separate mtd device which could be used for storing everything.