One is overcurrent protection:
I would recommend two on the firewall, an 80 or so for the alternator and a 40 for the battery feeder (providing you use a #8 jumper from the battery lug to the fuse block.) My reasoning on this is you do not want your "backup" feeder to accidentally pop EVER. So it is sized quite heavy for the sum of all loads plus a bit more.
Kevin also has a backup circuit for the Lightspeed EI, which made me slap my forehead over my leaving it off.
Here's the update with his additions. At some point I'll figure out how to make this diagram all nice and pretty. At the moment, it's written mostly in pencil. Click on the image to make it big.