Welcome to the site and sport! You definitely struck gold (comedic or otherwise) when you found this trove of knowledge known as DGCR.com! Lots of great tips/videos/instruction available (including video analysis, "In the Bag" type bag-contents breakdowns where users will help you put together the right combination of discs/plastics, TONS of personalized help here!), lots of great people on here with knowledge and a general desire to share it, and not to mention the huge database of courses!
Know this site, and know it well, for it will guide you to the promised land. (Y'know, like throwing 650' uphill in a headwind for a 'drop-in' deuce from 80').
On a more serious note, I will be curious to see how your back problems evolve through your disc golfing. I've found that unlike ball golf, walking EVERY round with your bag on, through generally rougher terrain than your average ball golf course can be a bit burdensome after a long week of playing 24+ holes every day. On the flipside, however, a round or two a week carrying a light load (15ish lb bag) and stopping to basically stretch and rotate/oscillate your spine each time you throw really strengthens your back and core, and can loosen up the tight muscles or creaky vertebraes. Use common sense and trust your body's warning signs.
If it feels like you're doing too much/going too hard, you probably are.
Keep your throws smooth, and don't worry about stepping into your throws (run-up, people will refer to this as the x-step, but often times it will include 2-3 steps, not just the single cross-step motion) too much at first. I, along with many others, will recommend the Driving with Dan Beato video as your first video mantra.
http://youtu.be/nED7gcXobEo
Finally, but most importantly, have fun!! check out the leagues that Prostar suggested, get involved and enjoy yourself! See you on the boards, dude!
