The squat and deadlift are great for the back, as long as you use proper technique. See Starting Strength by Rippetoe. You should be able to sit on any chair without back pain. An ergonomic chair is no answer --- it is a crutch that helps the problem grow.
Working out and weightlifting helps me too. You can't really lift in an olympic sense with bad mobility.
I try to do a combination of sitting and standing to keep my hips from getting too tight, which can end up creating an anterior pelvic tilt that will cause back pain. I'll do couch stretches[1] to open my hip flexors and banded pull-aparts[2] to alleviate some of the rounded shoulder issues that we all get from sitting and typing all day.
I recommend that before going to the gym and picking up the heaviest thing you can lift - focus on your core for a good 3 months. Do crunches (properly) and plank every day. When your core is more stable, then do indeed go pick up some heavy stuff (with proper form and a spot of course!).
Agree, I got into it and upped the weight pretty substantially and had injuries. Would not recommend. There's really no point to high weight. Moderation in all things... I can build a strong back with medium weight and more reps too.
Yes, proper form will be absolutely fine. But as the weight gets heavy for you, keeping a great form will be very difficult. You see many weight lifting olympians getting serious injuries.
