Congratulations on your soon-to-be chickens!
1) I'm putting woodshavings in the nest box, but do I just leave the floor of the coop bare? (It has a metal lined, pull out tray)
You will need something on the floor of the coop to make it easy to clean. More woodshavings will do nicely. This insulates it as said by ktc and also makes it much (much!) easier to clean their droppings off.
2) Is whole wheat or corn better or is there no difference?
Again I'll go with ktc here. You need a properly formulated food as their main diet - usually in pellet form but there are others available. Both wheat and corn can be fed in tiny quantities as treats. If the chickens fill up on them they will be missing out on the other nutrients in their main feed.
3) Is it OK to do the baked and crushed eggshells instead of oyster shell? Any more detail on how I do this and how much I should give them?
Assuming your chickens are already laying (or just about to start) most of the calcium they need is already in their food. It's usually recommended to give them extra shell grit (oyster or eggshell) in another container so they can just take what they need. So the quantity will depend on how much they choose to eat - just keep topping up the container when it gets low.
Personally I use crushed sea-shells but the instructions I've seen on here for egg shells are just to wash them and bake them (to kill any germs) and crush them (to make the bits unrecognisable as egg shells and small enough to swallow).
4) What are the essentials of first aid? Gentian violet sounds like it would be useful? Anything else?
Sorry, can't help you with the first aid question
5) Anything else I haven't thought of?
Just to re-check your coop and run
again for any gaps they can squeeze out of, and be really sure it's predator-proof! Good luck!