Nothing much you can do about it. Over time the keys collect oils from your fingers. For some people it’s not as much of an issue but if you eat while using your computer, rarely wash your hands or have sweaty hands, this will happen quicker. Turn the machine off, get a microfiber cloth and some eucalyptus oil and dapen the cloth with it and wipe the keys. Make sure the cloth isn’t wet so that any moisture gets into the keyboard area.
Eventually the machine should limit charging to 80% by itself to preserve the battery. You could also use an App called Al Dente to do the same. If you regularly use the full power of the machine, go with the permanent 140W charger, if you only use the machine for office tasks and rarely demand high performance of the machine, then go with the USB-C charging.
If you have a 15" model it is worth a bit less, somewhere around 500 - 700 USD but if you have a 16" model in good condition, I would say somewhere between 600 and 850 is a decent deal. https://www.ebay.com/sch/i.html?_from=R40&_nkw=macbook+pro+2019+i9&_sacat=0&LH_Sold=1&LH_Complete=1&rt=nc&LH_BIN=1
Short of buying a defective model and stealing the stabilisers I don’t think you can buy them anywehre, since they are not an individual part. However I know what you can make them yourself with a paper clip or equivalently thick wire. The typing feel also may not be much worse if you use them without the stabilser.
I use mine with a ThinkPad USB C dock, which works just fine. I also have a workstation with a Dell USB-C dock with ethernet and it works fine with M1 Pro. I would recommend to look for used business docks. I have seen some Elgato or ThinkPad docks for below £100.