I2C-to-SPI bridge and SD card
You will struggle to make this system work. An SD card offers a block-structured file system, which requires writes of full blocks of at least 512 bytes. Your bridge only supports 200-byte blocks.

Also the slow speed of I²C will give you trouble. Transferring 512 bytes over the 400&nbsp;kbit/s I²C link will take approximately 10&nbsp;ms. 

Finally, you will need to write a software driver layer to drive the SD card through the bridge. This will take a lot of effort.

I notice the PPC18F2580 has an SPI interface. You should use the SPI interface to talk to the SD card and use the I²C interface to talk to the sensors. There should not be a need for the bridge.