1976 20hp -200 start up info

As I posted earlier, I bought a 20 hp Merc that has set for about 15 years. It is not locked up.
It has electric start and the Ser# is 441xxxx.
My question is this. I plan on changing the spark plugs and the impellar. I will mix new gas as well. Is there anything else I should do before trying to start it?
I was thinking I would change the lower unit oil after I saw that it would run. Should I change it before trying to start it?

Anything else I should or should not do. I have run outobards for many years but this is my first motor that I have owned and my first time with one that has set for years.

Thanks

Re: 1976 20hp -200 start up info

If you can get it running perfect, you're really gonna love the power and speed of that motor! Be sure your transom is in good shape, because they are heavy and have tremendous torque. If you can borrow a compression gauge, I'd check it just to know now what it is. I'd clean the carb and change the fuel lines if you possibly could, although they have those darn crimped on lines that are expensive. If it has the cable operated choke, sometimes they stretch over time and won't totally close the choke plate and this causes them to be really hard to start. Get that choke to close right and good spark and they'll crank easily.
Other than the impeller, I wouldn't do much else until I was sure my electronics were good i.e. it runs well.
Thank goodness you have the stainless drive shaft on your motor.
I'd like to see a pic and a report on how you like it when you get it right.
COngrats on the purchase,
JBJ