The parts manual for the WF-4 and WG-4 is on the Wizard site here. about half way down is the parts manual free. The post right after it, is how to convert the part numbers into the last current mercury part numbers.
The instructions given for the operation of the WD-4S motor are good for the WG-4 also.
Use TC-W3 two cycle outboard motor oil in your fuel no thinner than 32:1 mix ratio. Some on this forum use 16:1 mix and others use 24:1. Since the WG-4 has needle bearings, I think 32:1 is just about right.
I second what Richard said, and you can get hard to come by parts on eBay by searching "Wizard outboard" and being patient. Lubriplate 105 is also available at Napa auto parts if you happen to have a store locally. Corn head grease is a substitute for lower unit grease also.
The Wizard wg-4 has many parts in common with the Mercury KD4. http://store.oldmercs.com/category_s/85.htm
If your water pump impeller is bad, you can get a new one made by Bob Scott.
You will need to send him the metal core from the old impeller. His contact information is here. Bob is a nice guy. just remember that this is not his main job and he does it out of love for the old motors.