I need around a week to transition a heavily data-driven website from one back end to another. During that time I do plan to attempt to keep some pages live, but they won't all work well or look brilliant. Some pages won't work at all.
What is the best way to ensure I don't scare Google? Should I hide everything from robots.txt, or mark everything that doesn't work as "503", or are there other things that I should be considering?