I've worked as a mechanic here and there and have a mechanic buddy who has said tons of times, "never do this for a living."
The basics
You'll get burned with hot exhaust, torches, welding
You'll get soaked the minute it rains or snows and there's no choice, you have to work under the car and fix it.
You better get good with that electrical etc, cause you'll have the oddest puzzles to solve.
Plan on scrapes, cuts and gashes, you'll get plenty of them
It's freezing cold crappy work in the winter
It's ball sweating hotter than hell in the summer around hot running cars with the fans blowing more heat your way.
Sound like fun so far?
Add that the lift wouldn't save your back, your back, back of your legs, etc etc are going to ache a lot of the time.
You'll spend a small fortune and owe tool guys for quite some time.
You'll likely get paid flat rate, which means if the job takes 10 hours...warranty pays 6.5 and it doesn't matter if it takes you 12 hours. You got 6.5 hours of pay.
Enjoy smelling the exhaust of cars running poorly, chemicals like brake cleaner etc etc...you'll be smelling them all day. It's only a set of lungs, no worries.
You'll blow black snot out of your nose all the time, cause you are around so much dirt and crud.