You should assume with the 8GB SSD
that about 3GB or so will be consumed by the OS and basic apps of the system leaving you about 4GB left to work with. You have to leave some free space, so once you go below 1GB of free disk, things will most likely start to slow down. I you can live with that, then you are fine. If you plan to load additional applications, then budget accordingly. If you never intend to open up the box and do upgrades, then you might want to order the 16GB SSD
to give you some growth space insurance. I've found my new mini to be much more usable as an every day laptop replacement than I thought when I ordered it. I keep finding more things I want to load on it. Looks like the 16GB SSD
I ordered isn't going to be enough, so I'm probably headed to an upgrade in the near future.
Also, make sure you get at least 1GB of memory. You might be able to boot inside of 512MB, but won't get much else in there after boot. I'm finding that my mini with XP is using about 350MB once everything gets loaded during the boot process. The WebCam software is pretty beefy, too, and that isn't even loaded in the 350MB.