1. I haven't tried it myself but I hear Meguiar's Scratch X
http://www.autogeek.net/megscratxfin.html is good for fine scratches. You can't go wrong w/ using any wax by Meguiar's or Mother's. Personally, I use Zymol. And I've heard Zaino is the mother of all waxes.
2. Which model do you have? The 2WD's have a 50L gas tank and the 4WD has a 45L capacity. I usually run my tank dry and avg. about 45L to fillup. By that point, the needle hovers between "E" (empty) and the gas warning light. I assume if your needle ever hits that warning light, you're really pushing your luck. To answer your question, I'd say from the moment the light goes on, you have approx. 100km (hwy mileage) left or 50-75km (city mileage). Keep in mind that I have the 6speed so if you have the 1ZZ you could probably beat that by a few more km's.
3. Type of gas is a touchy subject. People have their own preferences. Just stick w/ what you think works for you. My personal experiences have been Shell 91 as the equalizer (good mileage/good performance), Petro Canada 91 (great mileage/good performance) and Sunoco Ultra 94 (good mileage/great performance). I stay away from Esso.