Salary, IMHO is shitty at start but you will get increments once or twice each year, and that's way more than government increments. If you work hard, the increment would be 20,000 LKR.
Kinda. Many companies want you to work hard in irregular times. Not until 5.30, but it can be worse as mid-night. But that will pay off and usually comes with extra perks. If you are married, or about to get married soon, they can't assign you to those tasks
Don't be framed to PHP. How are you familiar with PHP5/OOP stuff? Can you nail down a ZEND certificate, have rep on stackoverflow.com, open source projects, etc?
A degree is not the sole criteria to land a job. Someone with several hundred commits in a famous PHP framework can land a job easily than some dumb guy who did an IT degree and has no experience in real world programming whatsoever. Try to complete a degree part time.
Trust me machan this is a well-funded field, and as long as you are honest, hardworking, a willing to learn, you'll be very happy you chose this path. I started my career when I'm 18, and I made my first 6-figure monthly income when I'm 20 (I'm 22 now). Age does not matter. Despite a real job, try to develop your online reputation. Create a site for yourself, lean new stuff, contribute to projects you love, help others, and do whatever it takes to increase your reputation. You will face some social issues that everybody thinks you are a poor jerk. Your family won't understand what on the earth you are doing to earn that much. You'll have hard times explaining the job to parents of your SO, but all it matters is how much happy you are.
Good luck!