from checking google 1 litre is correct , either 10/40 or 15/40 will do. changing oil is pretty important, my service book recommends every 5000 miles though I do mine a little more often as its only a 125 my bike only take 2 litres of oil so cost isnt really an issue like the bigger bikes. Its a good idea to change your oil filter at the same time, you dont have to but you might as well while your down there. I would say change your oil every 6 months as a guide, and dont get caught up in the fully synth, semi, dino, car or bike specific, 0 weight arguments, just stick some fresh oil in and ride it! ( when your leg allows ) I'm pretty sure that one of the more experienced members will chime in and give you better, more detailed and probably more correct advice but that is mine