@pugbutter You went a very long way to pointing out that I typed 'is' instead of 'isn't.' My wording was terrible, I wrote this at fairly late in the day for me. I admit that, you have my apologies for the confusion.
Now to answer the questions you asked:
While we cannot do a proper 'per session' experience gain, I have a number of ideas for how to distribute experience. Of course, this is somewhat open for debate from my players, depending on how they feel about it. We could do a somewhat even distribution, where all players receive experience per scene. That mechanic already exist within the game, and as long as I don't feel like the players are abusing it, I think it could work. Another option I have in mind would be more lump-sum experience gain, where players receive a fairly large chunk of experience at the end of each story arc. That option would be much more staggered and lurching, but I think still workable.
I'd considered the companion errata, but I won't lie, I've never played with it myself. One of the reasons I'm limiting this game, at least at the beginning, to the core rulebook is because my experience with the game as a whole is through a limited play group. My LGS is where I've mostly played this, and I'd be lying if I said it was the primary game of choice there. Thus, my actual experience with anything not in the core rulebook is basically non-existent.
And, strictly speaking, it's possible to be both a neonate And a thin-blood. It just means that your character being a thin-blood is more of a dark secret from their past, than actually relevant to the game's mechanics. Thin-bloods can commit diablerie and 'ascend' (for lack of a better term) to full vampire status, gaining a generation of 13 and a clan in the process. However, if a player wanted to play as a thin-blood proper, then I had planned to let them start with the bonus 15 exp but not the higher generation level.
If that shatters everyone's perception too greatly, though, I could just make you all start as fledglings. Hadn't planned on it, but far be it for me as the storyteller to not enable my players to be as pathetic and worthless as they want to be. Fairly easy fix from a story telling perspective, now that I think about it. Makes a few sticking points just go away.
So, actually,
@pugbutter. Everyone will be starting as fledglings now! I like your thinking. Any more oddly specific questions about my poor spelling?