You would not have to update your modem if you updated your router. They are separate and distinct devices and communicate with one another via ethernet and probably way faster than either your modem or router are capable of.
Do you know if your internet connection is cable or DSL? Cable protocols have changed in the last few years and my ISP updated my modem pretty much the same way I described my mesh router being upgraded. (I have also had two cable modems burn out which is why I now rent the modem rather than buy one. It worked cheaper in the long run. But that is another story.)
FWIW setting up my mesh router was a piece of cake. I used an app on my iPhone to give the network a name and password, and open an account with the router manufacturer (there is a small monthly subscription) and that was about it. The trickiest part was placing the other pucks to optimize the signal throughout the house and shop. But that was mostly trim and error. I would place a puck, wait for it to be discovered and join the net then a few days later use the app on my iPhone to check the signal quality and move it if necessary. Every week or so, the computer in Washington State reshuffles the interconnections based on traffic load and flow and that is about it. Once I got a phone call from the company that one of my pucks appeared to have failed, and they were sending a replacement.
