I've recently moved in with a friend who owns a shiny PS4 pro connected to our main TV. I have a trusty standard edition PS4 in my office. We both have our own seperate PS+ subscriptons. We own a mixture of games of disk and digital. We'd like to make it so that we can access each other's game libraries on both machines, and that if the pro is free, I should be able to pop downstairs and pick up one of my own games with my own save data right where I left off. How would we manage this most seamlessly?
While it is possible to do what you want, it is unfortunately not a very seamless process.
With physical (disk-based) games, this is no problem. Anyone can put any disk in any PS4 and play. It's much more complicated for digital games.
Unfortunately, accessing both your games on both machines will not be possible. Each of you will be able to access both your games on one machine only. This means you'll need to decide who gets to access both digital libraries on which console. To do that, you need to understand the principle of the "primary console".
Essentially, registering a PS4 as your "primary console" means that you're claiming that PS4 as "your PS4". Any family member, friend or guest can add their PSN account to your PS4 and play your games on their own account, but only if the games are already installed on the PS4, otherwise you need to download the games first. Family, friends and guests can only download and install their own digital games, and you can't access these.
Since multiple people can "own" the same PS4, you can both access each other's games on the same PS4, if you both mark the same PS4 as your "primary console". However, since each person can only "own" one PS4 at the same time, you won't be able to access each other's games on both consoles at once.
Fortunately, you can change the "primary console" as often as you want, as long as you have access to your current "primary console". For instance, if the PS4 Pro is the "primary console" for both of you, and your friend wants to play your games in the office, you'll have to unregister the PS4 Pro, then register the office PS4. If you no longer have access to the "primary console", you can still unregister it, but only once a month.
Accessing save data
Since you both have PS Plus, this should be quite a bit easier, as you'll both have access to cloud saves.
Unfortunately, automatic upload of cloud saves only happens once a day and only on your "primary console". From personal experience, the automatic syncing appears to be scheduled sometime around 4 AM. If the PS4 isn't online during that time, it won't try syncing until the next scheduled time (~24 hours later). There is no automatic download.
Thus, if you want to carry your save data over, you'll have to remember to upload it first, then download it on the next PS4.