Twenty fabrics is a nice amount but it's not a huge amount. If you want it to look scrappy, with each block a bit different, I'd go for wider strips. If you want all of your blocks to be identical, narrower strips. What you probably can't do is narrower strips *and* scrappy, I don't think you have enough fabrics for that, but I could be wrong.
Any idea what block size you like? Have you found a log cabin layout that appeals to you? That might determine the block size, which in turn could determine the strip size. Think about 6" or 12" blocks, to get you started.