Descent into Avernus teleportation circle questions

[Ettina]

I'm running Descent into Avernus, and the wizard PC is considering grabbing Teleportation Circle with their latest level up. I have a few questions.

For a PC who's traveled planes during the course of the adventure, would you have their free known teleportation circle sequences be ones on their current plane, or the plane they're most familiar with? What's the fluff for how the PC knows the sigil sequences they gain when learning the spell?

Does Elturel have a teleportation circle? If so, would it have survived the descent into Avernus?

What teleportation circles would exist in Avernus already?

[Unoriginal]

I'm running Descent into Avernus, and the wizard PC is considering grabbing Teleportation Circle with their latest level up. I have a few questions.

For a PC who's traveled planes during the course of the adventure, would you have their free known teleportation circle sequences be ones on their current plane, or the plane they're most familiar with? What's the fluff for how the PC knows the sigil sequences they gain when learning the spell?

Does Elturel have a teleportation circle? If so, would it have survived the descent into Avernus?

What teleportation circles would exist in Avernus already?

Elturel was definitively prosperous (or with access to a pious caster) and around long enough to have a teleportation circle. It would be placed in a building likely strudy enough to survive the Descent and of enough importance to have at least the Devils want it.

As for the other circles, well, Mordenkainen has a mage tower in Avernus, other casters could too. Furthermore, there are a lot of ruins on Avernus, anything from ancient temples to crashed Githyanki astral ships could have spell circles on it.

And that's not going into what the Fiends might have for many reasons.