Where should the first I-joist be set parallel to the rim board?
...usually if you read the 20-odd pages of documentation that come with your I-joists they will tell you what to do, and a great deal of what not to do. Or ask the person who punches the numbers into the computer to size &amp; select your specific I-joists what their layout program (based on the same manufacturer's data) expects you to do. The number of I-joists you get will be based on that. It's not common to just sell you I-joists at random - they are an engineered system and the specific series and size need to be chosen to fit your building loads - every place I know that sells them provides that service as part of the pre-sales process. 

One issue with "just a rim board" and then going (12/16/24 inches, depending on your layout specifics) is that the wall bearing on the rim board is wider (thicker) than the rim joist, and asking the floor-spanning plywood to carry the inside part of the wall load without direct support might lead to problems. Depending on the thickness of the wall, the first I-joist might want to be set at the inner face of the wall, rather than just sistered to the rim board. For a thin wall that might be the same, for a thick wall it might not.