How to approach insulating my rim joist
Actually you only want to use fiber insulation against cold surfaces (rim joist) when you can completely cut off the air supply from the interior.  Interior air carries a lot of water.  The air moves through the fiber insulation and condenses when it hits the rim joist and you have a potential issue.  

Better way is to buy a sheet of foam board insulation, like the blue or pink stuff, a can of spray foam insulation, and a roll of fiber insulation.  Cut the foam board so it fits loosely over the rim joist.  Fill in around it with the foam in a can.  Cover that whole thing with the fiber.  Now the dew point is inside the foam board where the air can't reach.  No condensation, really good insulation.  

If you want to get all geeky, you can calculate the dew point location in the assembly based on exterior and interior temps, interior relative humidity, and insulation type and thickness, to make sure the dew point is in the foam.  For example, don't use 1/4" foam board and R-30 fiber.  Use 2" foam board (about R10) and 6" fiber (about R19) and you should be OK.  

BTW, same principle applies to cold basement walls.  A nice layer of fiber insulation against the wall commonly creates a mold problem.