Amount of oil depends on which oil pan you have. I don't really go by an amount, I go by the dipstick. I try not to fill it to the Max or Full line. I try not to let it reach the lowest or IL low line. I try to keep it in the middle of these two lines. It is really very common for Airheads to run best with the oil about 1/2 Low, in between the two lines.
The dip stick is removed, wiped off and reinserted till the threads of the dip stick contact the top of the filler hole. Then remove to read.
Most will stay more stable around the halfway mark but these engines always use a little oil so you do have to keep an eye on it. Since this machine is new to you you should check the oil every day.
A cheap timing light with the clip on magnetic induction pick-up. It's the one that has a clamp arrangement to go on the spark plug wire. I thought the cheap Sears ones were $25 years ago. I have no idea what they are now. This is another tool you will need, so get it.