Put a new edge all the way across, then flip the blade over for a quick pass across the backside to remove burrs. If you don't have a grinding wheel, an inexpensive drill-mounted grinder can sharpen the blade right on the mower. Make sure the blade balances. If it was way out of balance, the whole mower would vibrate and shake all over. Bring it into balance by taking off a little more metal.
Most mowers have an oil drain plug underneath.
It's usually rusted shut. Instead, flip the mower on its side and drain the oil out through the filler hole. Refill with about 20 fresh ounces. Recommended oil is a 30-weight. In some conditions you can get by with 10-40.