I just can describe my workflow:
*) I set up the developer at twofold strength, i.e. I make 2,5 Liters out of a 5 Liter kit. This should further improve stability, and I dilute it to one-fold immediately before use.
*) I use boiled (and re-cooled) a.d. to minimize oxygen carryover
*) I store the two-fold working solution in full, airtight bottles in the dark (thick-walled, lab-quality PET plastic bottles with tight caps).
Under these circumstances, I can use the developer with predictable results for at least half a year. In fact, I prefer this to the hassle of diluting small amounts of developer for each film developing. At least one can be sure that a developer from a batch that worked well last week will do so also today and the next week.
I am not testing sensitometrically, only "by eye", but C41 is really stable stuff, as long as it is not oxidized by air (and it should be robust, as it can sit around in processing machines for weeks at 37C; with very low regeneration rates these days).
Another point: I have seen ads from a company, that sells ready-mixed C41 developer (also as a 2-fold concentrate) in canisters, so this stuff must be good for at least a few weeks.

Fixer is about the same as B&W fixer, and bleach should also keep well. Both are easy to test for functionality with B&W materials.

Georg