I’m sorry to hear of your misfortune. Be sure you have clearance from your doc and PT before doing any heavy lifting. Working on strength is a great fist step toward recovering normal function.
That’s correct that there are only 4 exercises we normally use in the early base period. That’s because the first 8 weeks of the base period are devoted to Max Strength. We normally use the Box Step Up/Pull Up couplet and either a Dip or Push up/Split Squat or Step Down. These are very basic exercises that work well for climbers. Max strength workouts need a lot of rest between sets and we know most climbers will not want to spend hours in the gym doing a routine. So we arrange as couplets of upper/lower body to shorten the rests a bit while still keeping close to the normal Max Strength protocol.
But this program is all designed for healthy people. In the case of recovering from a major injury and surgery you may be better off to spend a year doing more general and varied strength routines before focusing on max strength in a fe major muscle groups.
Steve and I have both had to recover from major injuries and I recommend a long general and core strength program. As you say, you’ve lost lots of strength in many areas. It will take a long time, years probably to correct some of this deficits and imbalances that arise from those weaknesses. Take the long view and proceed slowly and generally. You will get better just don’t expect miracles or speed results.