The Tesla Motors Club forum is an excellent resource for a deep dive into questions of this type. But that forum is so active the trick is figuring out which thread(s) to read.
Here's an extensive one on the subject of range loss over the years of ownership:
https://teslamotorsclub.com/tmc/threads/whats-your-90.50171/
You might also be interested in graphs of actual reported range loss vs. miles... or actually, kilometers. Several can be found here:
https://steinbuch.wordpress.com/2015/01/24/tesla-model-s-battery-degradation-data/
What problems have people had with their Tesla S.
That's a very broad subject. If you're really interested, you could spend days or even weeks reading discussions of various problems, some common and some rare, at the Tesla Motors Club forum.
You might want to check out Edmunds.com's long-term driving review, altho many of their problems were related to them having a relatively early production model; some problems have been fixed or at least occur less frequently, since then.
https://www.edmunds.com/tesla/model-s/2013/long-term-road-test/
(Warning: Links at that web page to the various articles are in reverse chronological order, so start at the bottom and work up to the top.)
You might also want to check out the various
Consumer Reports articles on the Model S, altho some (including myself) have questioned the sometimes apparently rather arbitrary nature of their ratings, which keep changing in a seemingly haphazard fashion. Those articles are a good source of info on what the more common problems are with the Model S. My advice: Pay attention to the details reported in the articles, but ignore the confusing and apparently self-contradictory ratings.