Hi Rob,
I'm impressed with the level of maturity shown in your post - that in itself is a good beginning. However, you should know that you're thinking of entering an industry with very little in the way of a career path or steady jobs, no matter what anyone tells you. That shouldn't stop you...but you do need to be aware of it.
The first thing you need to do is get a Class 1 medical. You're probably fine, but you don't want to spend loads of money and then find out you have some obscure thing wrong and can't be a commercial pilot. If that does happen there may be options in other countries ith less stringent medical requirements...but let's not cross that bridge unless you have to.
How, go
http://www.easyk.co.uk/kenyon/page4alt.htm. It'll tell you how to apply for Dennis Kenyon's scholarship, offering a PPL(H) each year to someone aged 17-23. That's definitely worth a try.
I can't tell you what to do, but for what it's worth, one of my early instructors started flying at 17. He didn't have anyone to pay for it, and his PPL took him two years. When I met him he was 26 and a fulltime instructor. Soon after he got a job on the North Sea. I heard a rumour some time afterwards that their sort of flying bored him...but hopefully it gave him enough experience and hours to get a different job. That's how it goes really, in the helicopter world - get your medical and qualifications, get adjob, build hours, try for something else, fingers crossed and hope for some luck along the way...
Hope that helps at least a little.