The clutch should be changed when it can't transfer all the energy from the engine to the wheels with out slipping, i.e. rpm's go up and speed stays the same. Its is all dependent on how you drive and how much you haul around. Easy starts and low shift rpm's will help let the clutch last. I have almost 180k on my Civic and still have the original clutch.
As for oil, starting off with regular oil will help the engine "break in." Since you are past that point, I would use a quality synthetic or something close to it. I used Mobile 1 which is labeled as a synthetic but is actually a blend of regular and syn oils. I liked it but for some reason I would have an oil consumption problem, burning in cyl. I recently changed to Royal Purple oil because I found a great deal on it and have no burning problems with it. Everything seems as good or better than with Mobile 1. I got my oil at http://www.clubrsx.com. They had the cheapest price and overnight shipping.
You should always use the minimum recommended octane level for your car. The engine will run with lower octane but at the cost of power and engine life to include possible catastrophic