I'm glad you like RS, but 12 hours a day is a lot. I don't want to tell you what's right and not, but 12 hours sitting in front of a computer screen is definitely unhealthy for your eyes, and your whole body.
OP, I've played RS for 8 years, but not a long time per day. I've had my days where I play for a long time, but most I play is 2-3 hours per day. It's taken me 3 years to max out my combat and some other skills. What I love is staking. I always end up winning a lot, losing about half of it, and then coming back and making more. I like the thrill of staking/pking. It's always a 50/50 gamble with staking, and I like my chances.
runescape!!!