Got some answers, but not all. My questions mainly come from the perspective of somebody who hosts club events every week.
Will all multiplayer events (including custom lobbies) require players to level up cars and unlock upgrades?
Sounds like they will, outside of spec racing. Made a thread about it.
Will public custom-made player lobbies be searchable via a lobby/server list, like they were in Forza Motorsport 4?
No answer, presumably no.
Are rolling starts supported in multiplayer?
No.
Will players be able to create timed races and if they are, will they work similar to real-life in that players have to complete their current lap to finish?
Yes on timed, no answer on how they finish, presumably the same as Forza Motorsport 7.
How have the vehicle collision physics improved since Forza Motorsport 7? In previous titles, cars felt very light when making contact with one another, causing them to easily spin out of control in certain scenarios.
No answer.
Will players be able to save lobby presets to make the creation and hosting of custom multiplayer races easier?
Yes.
Will Forza Motorsport feature Clubs and if so, what features will they have?
No answer, presumably no.
Will custom lobby hosts be able to limit who joins their races based on driver/safety level?
Unknown. No such options appeared in the footage of menu options.
Is there an area of the game where we can freely upgrade cars (ie: without being tied to the Car Mastery system) in order to explore, test and competitively balance them?
Sounded like a no.
Will there be a way for lapped players to be automatically ghosted?
Yes.
Will there be an option to ghost all players in a lobby for (only) the first lap of a race?
No, not lap specific.
Have any changes been made to the Vote to Kick system from Forza Motorsport 7?
No answer.
Will there be tools and resources in-game to each drivers proper racing etiquette?
No answer.
Will the “high speed collision predicted” ghosting system from Forza Horizon 5 be implemented into Forza Motorsport in any way?
No answer.