My wife is departing from 2E-K and I am departing from 2E-M a few hours later. How long can we stay together until we need to split up? Can I accompany her to her gate in K and them travel airside to my gate in M?
I don't think the odds are good that you can do this.
Layout-wise, the three halls (K/L/M) in 2E separate immediately after outbound Schengen passport control, before security. Hall K is straight ahead, while halls L and M have to be accessed via an automated train/people-mover that has one stop for each hall, each of which also has its own security checkpoint. I think you'll probably get stuck at the security checkpoint when you try to get to hall K with a hall M boarding pass.
Even if you get through, I'm doubtful there is a "straightforward" way to move from the airside departure area of hall M to the airside departure area of hall K, or indeed to even get out of the departure area at all, because there isn't normally a reason to do so -- arriving passengers are separated from departing passengers at 2E, and CDG enforces a security re-screening for arriving non-Schengen passengers before any connecting flight, so no one is disembarking directly into the departures area of (say) hall M who is looking to transfer to hall K for their connecting flight.
I might be wrong and would happily welcome corrections, but I'm doubtful you can accompany your wife to the gate, unfortunately.