How hard your quals are depends on how well you know your field. I went to a top 5 physics program, and everyone passed their qualifying exams, roughly half of whom opted to take the qual their first year of grad school. Obviously, we weren't randomly selected though.

Fellowships are a crapshoot that depend on a lot of factors outside your control, but getting funding is generally pretty easy in the sciences. When you work as an "RA" you are basically just doing your thesis research. TAing can be time consuming, but literally no one cares if you do it poorly, so it's not high pressure.

But this is a red flag:

Let’s assume you have the financial aspect of your PhD taken care of (e.g. You have an easy/enjoyable TA job). What other requirements are there other than passing Quals? Could I read interesting books indefinitely until I find something interesting to publish?

That isn't how research works, at least in the sciences. Research is generally 1% "big idea" and 99% slowly grinding it out to see if it works. Your adviser, if he/she is any good, will help you find a big idea that you can make some progress on and you'll be grinding it out every week and meeting with your adviser or other collaborators if you've gotten stuck.

That said, a bad adviser probably won't pay any attention to you. So you can do whatever you want for about 7 years until people realize you've made no progress and the wheels come off the bus (at which point they'll probably hand you a masters degree and send you on your way).