1. Why did you go to grad school?

I liked doing research -- I'd started as an undergraduate and wanted to do more. And I wanted to learn more quantum mechanics and apply it to models to understand some (approaching...) real world problems. I liked the place, the research and the atmosphere and fellow graduate students.

2. When did you go to grad school?

I went straight after undergraduate, age 22. Finished just over a year ago.

3. What is a good reason to go to grad school?

I think about the only reason to go to grad school is that you like doing research and/or learning the subject to greater depths whilst on the front lines, worry about and performing the nitty-gritty side of things.

4. What is a bad reason to go to grad school?

Expand career opportunities. To stay a student. To get "Dr." in front of your name.

5. What is the best state of mind to start grad school?

Be open minded about what you're researching and focussed on the task at hand. Treat it like a job: when you're in the office/lab/library, don't procrastinate and waste time. Do stuff. Take time off; go on vacation. Watch your mental and physical health. Both of these things can suffer in grad school -- if they are, take a step back, take some days off, make time to do fun stuff. Don't work yourself to the bone -- life is short and you should be doing fun stuff and enjoying some of the freedoms that grad school gives you.

6. What obvious and not so obvious things should I look for when choosing a program?

Assuming STEM, as this is my background: supervisor is the most important person. Try to find someone who you get on with; a strained relationship with supervisor definitely makes life more difficult (I had some experience here). Find out about money for traveling to conferences etc. Work environment (will you be in cubicle farm? small shared office?) and atmosphere (is everyone in 14hrs a day, 7 days a week? are people happy? do people look permanently tired/ill?). Talk to grad students 1-to-1 away from faculty to get some honest perspective on pros/cons of the place -- most will be happy to give you the low-down. If profs don't give you time/space to talk to grad students whilst at interview, take this as a bad sign.

7. How on earth am I supposed to generate income while simultaneously committing enough hours to my studies? During the school year in undergrad I worked usually less than 10 hours a week.

Again, from a STEM perspective, you'll be earning money. Probably not great money, but enough to live off. Many places (if you're a full-time grad student) won't allow you/be at all happy with you having another job. I know in my contract that I signed, it explicitly stated I couldn't have a second job. Often you can make some extra money teaching/TAing for classes, although the hourly pay is rough in reality.