Things will be unexpectedly closed. Critical resources will go on one-day strikes, announced or unannounced. Churches and museums will be chiuso per restauro. And Some Other Damn Thing Will Happen.
When you arrive in Rome, make a shopping list -- things would want to see, where they are located, when you think they will be open. Organize it by city quadrants. Set off. Be opportunistic.9 When the inevitable setbacks occur, immediately change plans, taking stock only at day's end.