Happy to gift you the society moduls, DM me

Pf2 is pretty balanced, if its in the rules, you should be fine

As a pf GM, i would allow it, but not a fully fledged elder dragon, of course. Well, maybe a very old elder dragon with hip problems, complaining about the youth,that would be fun.

But something small, young, sure. You just need to balance it and if the player gets top cocky, there are always dragon hunters around.

Maybe have a look at the Battlezoo: Dragons 3rd Party book, they did a good job in balancing Dragons as a playable ancestry.

I found Pathfinder society scenarios are a good Start. 2 or 3 encounters, most are done in 2 hours, easy to adapt. Way less pressure than a 20 level run.