I think we’d all benefit from general advice, but I mean how much about what it would really be like, versus their expectations, would you want them to know?

That's all young me would need to know. Some amount of wide-eyed plunging in is essential for the young writer. The naivete keeps you going and by the time you realise what a cesspool you're in, it's too late to back away. Then you learn the hard lesson: most of what you write won't matter.