Would be interested how you bridge potential pcs, or is it more like runequest?
Not sure what you are asking, but generally when starting a campaign I try to get PC creation started about two weeks before I plan to have the first session, and we go through an iterative process where they submit a potential background and we start jointly refining it until the PC is grounded in the setting, and the player has some idea of the character's role in the setting. Also, since my original goal was to provide myself a setting that I could set whatever modules I purchased in, but which made more sense geographically and culturally than any of the resources I had access to, a lot of the core Tolkien inspired consensus fantasy still works. There might be some unique features to being an elf in Korrel, but you're still fundamentally in the umbrella of post-Tolkien elvishness.
I also try to start campaigns in areas which are easier for players to relate to and more like consensus fantasy, and then start gradually introducing ideas to the players. For example, players may come to learn that buildings often are sentient, and have spirit that reflects the character of those that have inhabited them, and the longer that a building has been inhabited and the more consistent the character of those that have inhabited them, the stronger, more active, and more intelligent this spirit is. Then at some point down the line they might solve a murder mystery by asking the house who it was that entered it at 2 o'clock in the morning, because they realize that the house penetrated the disguise self spell the murderer was using to throw them off the trail even if the butler did not. Or they may learn that the forces of good are responsible for putting up a barrier around positive energy that prevents it from being directly manipulated by mortal magic, and this is why wizards cannot heal, and then they may eventually learn that the bad guy's goal is to find some way around this barrier and get a source of positive energy that he may then empower arcane spells with. I don't try to dump all this bits of how the world works on the players all at once.
The weirder and more alien areas I tend to avoid gaming in both because I recognize that it would be a challenge for the players to fit in, and a challenge of world building for me to really make it work right. Mostly in practice those areas intersect the game in the form of colorful NPCs with alien cultures and outlooks.