polyglot:
I don't see any actual questions, so I don't know what help you're looking for. You seem to have decided on some hardware, therefore you need to acquire one of each (SD, Ethernet, etc) bit of hardware and write a simple Arduino program to talk to each device. Then integrate them all together with whatever control logic you want.Better yet, think like an engineer and be more formal in your design. Google up "requirements analysis" and "functional/physical allocation", draw out your functional flow diagram, etc. Then you will understand what you are doing and the only remaining questions should be device-specific things.
We can't do your design for you.
I am in an engeneing class. I have diagrams/charts. I'm just making sure I'm noting going to get screwed.