Make enough to be able to write full-time (unfortunately, either me or my wife will need a job with healthcare benefits because stupid American healthcare system). Honestly, I'd be perfectly happy being able to trundle to my laptop every day, bang out 1500-2000 words and humbly submit a new book to the uncaring masses, hoping that enough folks like it that I can keep on doing that every month.
If things really took off, life would be pretty similar, just a little easier ... spend a few weeks in the winter within driving distance of the Florida beaches and Magic Kingdom/Universal, do a few cons (more for fun and to meet cool people, but some selling ... I really love public speaking, so I'd be totally up for doing lots of panels), go on modest vacations. But ultimately, write those chapters every day and keep on doing that.
Harry Potter success initially seems appealing ... but with a little thought, seems like it would be more of a burden than anything. I would be perfectly happy being just successful enough that the occasional fan recognizes me but being anonymous. Things like movies and video games and comic books and action figures tickle my nerd fancy, but that means a lot more time spent administrating/supervising/collaborating, and honestly, I am perfectly happy just doing my own little thing and publishing it.