Basic Questions about '89 RM250

Hi guys! I just bought an 89 RM250 and need some basic info on it so i can hit the trails. 1. What is the gas/oil mix ratio? 2. What type of engine oil should i use and how much do i put in (there is no looking glass for the oil???)? 3. What is used to fill the rear shock (air, nitrous?)? If its not just plain air, what would happen if i filled it with air? The shock is blown and i want to try to refilling it before i attempt rebuilding it.
Any info would be appreciated