Your fuel/oil ratio should be 50:1 after Pappy's recommended extra oil with the first tank. Use a TC-W3 grade marine motor to mix with the gas (87 octane)
Change your fuel line to ethanol resistant type. Napa or Autozone with have the fuel lines to replace the ones on the motor. The older fuel lines deteriorate with the use of ethanol enriched gasoline.
Spark plugs Champion J4C or J6C, depending if you are going to do a lot of low trolling or not.
Clean and gap the points to 0.020 (You can get points file at Napa or small engine shop for cheap!!)
Gap the spark plugs to 0.030
Change your gear oil and make sure there are the plastic washers under the drain and fill screws. Do not mess with the phillips head screw or you might have to take apart the gearcase to get it to function again. Please make sure there is only one plastic/Fiber washer sealing the gearcase, because 2 back to back will allow water intrusion into the gearcase.
If you do not live near a Evinrude dealer and can not get the gear oil Pappy recommended, then a good quality marine grade 80-90wt gear oil will do. This can be found at Wal Mart, Academy, Napa, or Auto Zone....etc.
If you are uncertain when the impeller has been change, then replace it or have it replaced. Any old impeller might pump water at first, but decided to break apart at the lake while running and burn up and seize your motor.
Always start the motor in water, if you do not you will damage your impeller and possibly overheat the heat and seize it up/damage it. Ear muffs won't work!!! Put the motor in a barrel or on the back of a boat on the lake. Make sure the level of the water is a good 3 or 4 inches above the water pump. It is where the gearcase bolts onto the exhaust housing. The tale tell is the exhaust relief at back of motor housing. It is a piece of corrugated thick black tubing. There will be thick spray of exhaust and water.
Here is link that will give you a little bit better understanding.
https://www.sschapterpsa.com/ramblings/OMC_9.5.htm
Good luck!!