It's outlined in the Kodak literature. See here, page 2-2 (page 19 in the pdf), table lower right corner: https://imaging.kodakalaris.com/sites/default/files/wysiwyg/pro/chemistry/z130.pdf
I would recommend reading the documentation on the materials you use. Especially color chemistry from the major brands (i.e. Kodak & Fuji) are usually documented very, very well. All of your questions are answered by this documentation.
Personally I keep an eye on the manufacturer's data as well as pH as from experience I know that pH drift of the developer is the first thing to occur in my open tray development process. This may be different from a slot or roller transport approach. YMMV. In case of doubt, stick to the manufacturer's data and keep in mind those are also based on continuous usage / high volume, so don't expect everything to be fine and dandy if you get your developer from a closet after sitting unused in storage for 2 weeks.
Don't wait until you get visual clues of poor developer condition; you're too far by then. It'll usually show up initially as lack of pure blacks (they tend to go blue) and perhaps a mild magenta/green shift. However, generally by the time you notice this, you might go back through the preceding prints and notice in hindsight that they're all compromised...hence the recommendation to not wait for problems to arise.
For more info/documentation go here and scroll down to the bottom of the page: https://imaging.kodakalaris.com/retailers/equipment/chemistry-agx/ektacolor-chemicals
This really is required reading if you're doing RA4 development.
