Forgot to mention: with just the Encumbering quality and the Primitive gear type, you can get the following spread of IR ratings:
2 (1xLI [Starter if you want to add another quality])
4 (2XLI, 1xLI+E [Starter if you want to add another quality])
5 (1xSI [Starter])
6 (3xLI, 2xLI+E)
7 (1xSI+1xLI, 1xSI+E [Starter])
8 (3xLI+E)
9 (1xSI+2xLI, 1xSI+1xLI+E)
11 (1xSI+2xLI+E)
EDIT: The reason why the primitive gear type is limited in this way is that it cannot get Greater Improvements, and in its place it gets a Lesser Improvement. You can shift those Improvement slots (gear gets 3, for balance/sanity check reasons) down, but never up.
Gear that could get 2 SI would have the following chart:
2 (1xLI [Starter if you want to add another quality])
4 (2xLI, 1xLI+E [Starter if you want to add another quality])
5 (1xSI [Starter])
6 (3xLI, 2xLI+E)
7 (1xSI+1xLI, 1xSI+E [Starter])
8 (3xLI+E)
9 (1xSI+2xLI, 1xSI+1xLI+E)
10 (2xSI)
11 (1xSI+2xLI+E)
12 (2xSI+1xLI, 2xSI+E, 1xGI)
14: (2xSI+1xLI+E, 1xGI+1xLI, 1xGI+E)
17: (1xGI+1xSI)
19: (1xGI+1xSI+1xLI, 1xGI=1xSI+E)
21: (1xGI+1xSI+1xLI+E)
That means that you have 23 possible permutations over 14 possible results (and my math may be off because it's now 12:15 AM here).
EDIT 2: Actually, the numbers above assume you don't do 0 IR, which would include 12 new permutations if I remember my basic math right. Right now I have six armor qualities excluding Encumbering, which range in cost. I have certainly not filled that list. The number of possible interesting armor combinations is likely in the hundreds even before you include 0-protection armor (fire-proof spacesuit!)