1. SUP 720 will need to be palce in either slot5/6. So you need to consider cabling if the currnet slot 5/6 is occupied.

2. Take backup and verify the config as some commands might not have been applied.

3. Check if the existing power supplies and fan trays meet requirements.

4. Sup720 supports only IOS mode, so if your current sup1,1A is in hybrid or CATos mode, there is a whole lot of steps you should perform to convert the configuration.