“Problem though, I was trying to check the oil level and I don`t see anything at all (the bike is upright and has been warmed). The view screen is all black…am I doing something wrong or does it just mean that the engine oil is maxed out”
If it’s a used bike and the oil level viewing window is all black, I’m guessing that it’s full of oil but the oil may be dirty
Look at the window when the bike is on the sidestand. It should appear empty or at least less than full (assuming that the window is on the right-hand side of the engine).
Whatever, if it’s a used bike, get the oil and filter changed anyway unless you have service records to prove that it was changed at the most recent service interval. It is VERY important to ensure that there is enough oil in the bike as if there isn’t, the engine could seize and you could very likely be thrown to your death. Too much oil isn’t good either, but not so potentially dangerous.
BTW: you shouldn’t need to take anything off the bike to clean, lubricate or check the chain tension.