(in very loose order!)
1. Decide on UK or American spelling
2. Decide on page naming conventions
3. Decide on pairing style conventions
4. Finalize infoboxes
5. Figure out how lists are going to work
6. Make sure that newbies can jump right in (make a style guide, make page templates, etc)
7. Finalize all categories
8. Finalize site theme and top menu
9. Announce Grand Opening on /r/HPFanfiction and /r/harrypotter
10. PROFIT!
Anything I missed?