Game worlds without the system attached to it
If you are willing to put in the time and effort you can pretty much move any setting to a different game system. Some are easier to do than others of course, but it is possible.
As for Faerun I'd start before the Time of Troubles and just play organically, don't assume what happened in the novels happens in your Faerun....I remember when the original boxed set came out, and how wonderful it was to read the material....lot of good there...
Same with Oerth.....start with the box set (the original one) and then just move from there ignoring the subsequent novels etc...