Don't buy a keyboard cover. Buy a can of compressed air. I've occasionally had a soft-feeling spacebar on my MBP 2016 that was fixed with a few bursts of air, and this also seems to be Apple's recommended intervention. I've never had any issues I'd consider severe though, so perhaps there are more significant issues I've yet to encounter.
And I wouldn't buy AppleCare, even if you believe that this generation of MBPs is abnormally problematic. In theory if there are serious problems with these (unanticipated by Apple) then AppleCare could be worth it, but in my experience if there are serious design flaws then you will get free service regardless. That is what happened to me a number of years ago (~2010) when my MBP had serious graphics issues. Apple replaced the mainboard for free even though I didn't have AppleCare. Maybe policies have changed, or that was a special exception, but I've never purchased AppleCare in my 15 years of Mac ownership and I've never had repairs that cost anything near what I'd have paid for AppleCare over all those years.