do i need to do anything other than change the oil and put new spark plug in?
You might want to check and clean the air filter and check the oil level in the differential.
how much oil do i need to put back?
1.7 quarts. Make sure you use an oil designed for wet clutches. Most automotive oils have friction modifiers that will make the clutch slip. The recommended oil is Honda GN4.
Most 4-wheeler problems are caused by a loose nut connecting the handlebars and the seat!!
You only need two tools in life -- WD-40 and duct tape. If it doesn't move and should, use the WD-40. If it shouldn't move and does, use the duct tape.