Answer
A few additions worth adding to that checklist: make sure the operating system itself has all its own known patches installed (not just IFS's own prerequisites); take a database backup using the RMAN utility specifically, on whatever environment you're about to install into; back up the middleware environment using IFS's own deployed backup script; and if the servers are virtualized, take a VM snapshot as well, as a fast rollback option on top of the formal backups. Combining a proper RMAN/middleware backup with a VM snapshot gives you both a supported recovery path and a fast one if something goes wrong mid-installation.