It is likely that the 2k edge you get with the green brick would be adequate for most knives, so I would either focus on stropping stuff (for finishing) or something more coarse in case you need more metal removal than the 2k stone provides. Really, the need to go any higher depends on what you are cutting or simply your interest in a higher finish level.
You can really strop on just about anything (newspaper, jeans, or other stuff).
That said, I would choose either or both of these:
Great Strop Set http://www.chefknivestogo.com/haamstkit.html
Coarser Stone http://www.chefknivestogo.com/beston500.html
one of my favorites http://www.chefknivestogo.com/la400grst.html
If you really want a finer stone after the 2K Green Brick, then I love my Kitayama 8K and it really does a great job polishing the edge http://www.chefknivestogo.com/kitayama8000.html
- $78 or a Suehiro Rika 5K if the extra $28 is too much for your budget http://www.chefknivestogo.com/suri50grst.html
- $50. I have both and they are both really great, but coming off the 2K brick my vote goes to the Kitayama.
I hadn't considered the combo stones that Melampus points out . . . that is another way to go. I don't have experience with those, so I cannot compare. I can also second the vote for the 1K UME as an AWESOME stone, but if you go that route then I would not recommend the brick, instead likely the Rika noted below.