For Cokin filters, there's basically 3 components. The filter holder, an adaptor ring, and then the filters themselves. They make various "series" based on different sizes of filters. The P-series is pretty standard, although for an UWA on a full frame camera, you'll probably experience vignetting with their standard P-series holder. They make a "slim" holder which apparently can be used down to 20mm without vignetting. Note that the regular holders will hold 3 filters and the slim only 1.
I don't believe Cokin makes 10 stop ND filters. They do 1-stop, 2 stop and 3 stop, IIRC. Although with a regular holder you could theoretically stack 3 3-stop NDs. Although I wouldn't necessarily recommend that as you'll probably degrade your image a lot.
Cokin filters tend to be at the cheap end (typically ~$25 a filter, plus holders and adaptors).
The other option is Lee filters. Lee filters are better quality than Cokin, but considerably more expensive (closer to $100 a filter). If you have the cash, go for Lee, otherwise Cokin is your best bet.